diff --git a/CHANGELOG.md b/CHANGELOG.md new file mode 100644 --- /dev/null +++ b/CHANGELOG.md @@ -0,0 +1,5 @@ +# Revision history for k8s-wrapper + +## 0.1.0.0 -- 2022-03-13 + +* First version. diff --git a/LICENSE b/LICENSE new file mode 100644 --- /dev/null +++ b/LICENSE @@ -0,0 +1,373 @@ +Mozilla Public License Version 2.0 +================================== + +1. Definitions +-------------- + +1.1. "Contributor" + means each individual or legal entity that creates, contributes to + the creation of, or owns Covered Software. + +1.2. "Contributor Version" + means the combination of the Contributions of others (if any) used + by a Contributor and that particular Contributor's Contribution. + +1.3. "Contribution" + means Covered Software of a particular Contributor. + +1.4. "Covered Software" + means Source Code Form to which the initial Contributor has attached + the notice in Exhibit A, the Executable Form of such Source Code + Form, and Modifications of such Source Code Form, in each case + including portions thereof. + +1.5. "Incompatible With Secondary Licenses" + means + + (a) that the initial Contributor has attached the notice described + in Exhibit B to the Covered Software; or + + (b) that the Covered Software was made available under the terms of + version 1.1 or earlier of the License, but not also under the + terms of a Secondary License. + +1.6. "Executable Form" + means any form of the work other than Source Code Form. + +1.7. "Larger Work" + means a work that combines Covered Software with other material, in + a separate file or files, that is not Covered Software. + +1.8. "License" + means this document. + +1.9. "Licensable" + means having the right to grant, to the maximum extent possible, + whether at the time of the initial grant or subsequently, any and + all of the rights conveyed by this License. + +1.10. "Modifications" + means any of the following: + + (a) any file in Source Code Form that results from an addition to, + deletion from, or modification of the contents of Covered + Software; or + + (b) any new file in Source Code Form that contains any Covered + Software. + +1.11. "Patent Claims" of a Contributor + means any patent claim(s), including without limitation, method, + process, and apparatus claims, in any patent Licensable by such + Contributor that would be infringed, but for the grant of the + License, by the making, using, selling, offering for sale, having + made, import, or transfer of either its Contributions or its + Contributor Version. + +1.12. "Secondary License" + means either the GNU General Public License, Version 2.0, the GNU + Lesser General Public License, Version 2.1, the GNU Affero General + Public License, Version 3.0, or any later versions of those + licenses. + +1.13. "Source Code Form" + means the form of the work preferred for making modifications. + +1.14. "You" (or "Your") + means an individual or a legal entity exercising rights under this + License. For legal entities, "You" includes any entity that + controls, is controlled by, or is under common control with You. For + purposes of this definition, "control" means (a) the power, direct + or indirect, to cause the direction or management of such entity, + whether by contract or otherwise, or (b) ownership of more than + fifty percent (50%) of the outstanding shares or beneficial + ownership of such entity. + +2. License Grants and Conditions +-------------------------------- + +2.1. Grants + +Each Contributor hereby grants You a world-wide, royalty-free, +non-exclusive license: + +(a) under intellectual property rights (other than patent or trademark) + Licensable by such Contributor to use, reproduce, make available, + modify, display, perform, distribute, and otherwise exploit its + Contributions, either on an unmodified basis, with Modifications, or + as part of a Larger Work; and + +(b) under Patent Claims of such Contributor to make, use, sell, offer + for sale, have made, import, and otherwise transfer either its + Contributions or its Contributor Version. + +2.2. Effective Date + +The licenses granted in Section 2.1 with respect to any Contribution +become effective for each Contribution on the date the Contributor first +distributes such Contribution. + +2.3. Limitations on Grant Scope + +The licenses granted in this Section 2 are the only rights granted under +this License. No additional rights or licenses will be implied from the +distribution or licensing of Covered Software under this License. +Notwithstanding Section 2.1(b) above, no patent license is granted by a +Contributor: + +(a) for any code that a Contributor has removed from Covered Software; + or + +(b) for infringements caused by: (i) Your and any other third party's + modifications of Covered Software, or (ii) the combination of its + Contributions with other software (except as part of its Contributor + Version); or + +(c) under Patent Claims infringed by Covered Software in the absence of + its Contributions. + +This License does not grant any rights in the trademarks, service marks, +or logos of any Contributor (except as may be necessary to comply with +the notice requirements in Section 3.4). + +2.4. Subsequent Licenses + +No Contributor makes additional grants as a result of Your choice to +distribute the Covered Software under a subsequent version of this +License (see Section 10.2) or under the terms of a Secondary License (if +permitted under the terms of Section 3.3). + +2.5. Representation + +Each Contributor represents that the Contributor believes its +Contributions are its original creation(s) or it has sufficient rights +to grant the rights to its Contributions conveyed by this License. + +2.6. Fair Use + +This License is not intended to limit any rights You have under +applicable copyright doctrines of fair use, fair dealing, or other +equivalents. + +2.7. Conditions + +Sections 3.1, 3.2, 3.3, and 3.4 are conditions of the licenses granted +in Section 2.1. + +3. Responsibilities +------------------- + +3.1. Distribution of Source Form + +All distribution of Covered Software in Source Code Form, including any +Modifications that You create or to which You contribute, must be under +the terms of this License. You must inform recipients that the Source +Code Form of the Covered Software is governed by the terms of this +License, and how they can obtain a copy of this License. You may not +attempt to alter or restrict the recipients' rights in the Source Code +Form. + +3.2. Distribution of Executable Form + +If You distribute Covered Software in Executable Form then: + +(a) such Covered Software must also be made available in Source Code + Form, as described in Section 3.1, and You must inform recipients of + the Executable Form how they can obtain a copy of such Source Code + Form by reasonable means in a timely manner, at a charge no more + than the cost of distribution to the recipient; and + +(b) You may distribute such Executable Form under the terms of this + License, or sublicense it under different terms, provided that the + license for the Executable Form does not attempt to limit or alter + the recipients' rights in the Source Code Form under this License. + +3.3. Distribution of a Larger Work + +You may create and distribute a Larger Work under terms of Your choice, +provided that You also comply with the requirements of this License for +the Covered Software. If the Larger Work is a combination of Covered +Software with a work governed by one or more Secondary Licenses, and the +Covered Software is not Incompatible With Secondary Licenses, this +License permits You to additionally distribute such Covered Software +under the terms of such Secondary License(s), so that the recipient of +the Larger Work may, at their option, further distribute the Covered +Software under the terms of either this License or such Secondary +License(s). + +3.4. Notices + +You may not remove or alter the substance of any license notices +(including copyright notices, patent notices, disclaimers of warranty, +or limitations of liability) contained within the Source Code Form of +the Covered Software, except that You may alter any license notices to +the extent required to remedy known factual inaccuracies. + +3.5. Application of Additional Terms + +You may choose to offer, and to charge a fee for, warranty, support, +indemnity or liability obligations to one or more recipients of Covered +Software. However, You may do so only on Your own behalf, and not on +behalf of any Contributor. You must make it absolutely clear that any +such warranty, support, indemnity, or liability obligation is offered by +You alone, and You hereby agree to indemnify every Contributor for any +liability incurred by such Contributor as a result of warranty, support, +indemnity or liability terms You offer. You may include additional +disclaimers of warranty and limitations of liability specific to any +jurisdiction. + +4. Inability to Comply Due to Statute or Regulation +--------------------------------------------------- + +If it is impossible for You to comply with any of the terms of this +License with respect to some or all of the Covered Software due to +statute, judicial order, or regulation then You must: (a) comply with +the terms of this License to the maximum extent possible; and (b) +describe the limitations and the code they affect. Such description must +be placed in a text file included with all distributions of the Covered +Software under this License. Except to the extent prohibited by statute +or regulation, such description must be sufficiently detailed for a +recipient of ordinary skill to be able to understand it. + +5. Termination +-------------- + +5.1. The rights granted under this License will terminate automatically +if You fail to comply with any of its terms. However, if You become +compliant, then the rights granted under this License from a particular +Contributor are reinstated (a) provisionally, unless and until such +Contributor explicitly and finally terminates Your grants, and (b) on an +ongoing basis, if such Contributor fails to notify You of the +non-compliance by some reasonable means prior to 60 days after You have +come back into compliance. Moreover, Your grants from a particular +Contributor are reinstated on an ongoing basis if such Contributor +notifies You of the non-compliance by some reasonable means, this is the +first time You have received notice of non-compliance with this License +from such Contributor, and You become compliant prior to 30 days after +Your receipt of the notice. + +5.2. If You initiate litigation against any entity by asserting a patent +infringement claim (excluding declaratory judgment actions, +counter-claims, and cross-claims) alleging that a Contributor Version +directly or indirectly infringes any patent, then the rights granted to +You by any and all Contributors for the Covered Software under Section +2.1 of this License shall terminate. + +5.3. In the event of termination under Sections 5.1 or 5.2 above, all +end user license agreements (excluding distributors and resellers) which +have been validly granted by You or Your distributors under this License +prior to termination shall survive termination. + +************************************************************************ +* * +* 6. Disclaimer of Warranty * +* ------------------------- * +* * +* Covered Software is provided under this License on an "as is" * +* basis, without warranty of any kind, either expressed, implied, or * +* statutory, including, without limitation, warranties that the * +* Covered Software is free of defects, merchantable, fit for a * +* particular purpose or non-infringing. The entire risk as to the * +* quality and performance of the Covered Software is with You. * +* Should any Covered Software prove defective in any respect, You * +* (not any Contributor) assume the cost of any necessary servicing, * +* repair, or correction. This disclaimer of warranty constitutes an * +* essential part of this License. No use of any Covered Software is * +* authorized under this License except under this disclaimer. * +* * +************************************************************************ + +************************************************************************ +* * +* 7. Limitation of Liability * +* -------------------------- * +* * +* Under no circumstances and under no legal theory, whether tort * +* (including negligence), contract, or otherwise, shall any * +* Contributor, or anyone who distributes Covered Software as * +* permitted above, be liable to You for any direct, indirect, * +* special, incidental, or consequential damages of any character * +* including, without limitation, damages for lost profits, loss of * +* goodwill, work stoppage, computer failure or malfunction, or any * +* and all other commercial damages or losses, even if such party * +* shall have been informed of the possibility of such damages. This * +* limitation of liability shall not apply to liability for death or * +* personal injury resulting from such party's negligence to the * +* extent applicable law prohibits such limitation. Some * +* jurisdictions do not allow the exclusion or limitation of * +* incidental or consequential damages, so this exclusion and * +* limitation may not apply to You. * +* * +************************************************************************ + +8. Litigation +------------- + +Any litigation relating to this License may be brought only in the +courts of a jurisdiction where the defendant maintains its principal +place of business and such litigation shall be governed by laws of that +jurisdiction, without reference to its conflict-of-law provisions. +Nothing in this Section shall prevent a party's ability to bring +cross-claims or counter-claims. + +9. Miscellaneous +---------------- + +This License represents the complete agreement concerning the subject +matter hereof. If any provision of this License is held to be +unenforceable, such provision shall be reformed only to the extent +necessary to make it enforceable. Any law or regulation which provides +that the language of a contract shall be construed against the drafter +shall not be used to construe this License against a Contributor. + +10. Versions of the License +--------------------------- + +10.1. New Versions + +Mozilla Foundation is the license steward. Except as provided in Section +10.3, no one other than the license steward has the right to modify or +publish new versions of this License. Each version will be given a +distinguishing version number. + +10.2. Effect of New Versions + +You may distribute the Covered Software under the terms of the version +of the License under which You originally received the Covered Software, +or under the terms of any subsequent version published by the license +steward. + +10.3. Modified Versions + +If you create software not governed by this License, and you want to +create a new license for such software, you may create and use a +modified version of this License if you rename the license and remove +any references to the name of the license steward (except to note that +such modified license differs from this License). + +10.4. Distributing Source Code Form that is Incompatible With Secondary +Licenses + +If You choose to distribute Source Code Form that is Incompatible With +Secondary Licenses under the terms of this version of the License, the +notice described in Exhibit B of this License must be attached. + +Exhibit A - Source Code Form License Notice +------------------------------------------- + + This Source Code Form is subject to the terms of the Mozilla Public + License, v. 2.0. If a copy of the MPL was not distributed with this + file, You can obtain one at http://mozilla.org/MPL/2.0/. + +If it is not possible or desirable to put the notice in a particular +file, then You may include the notice in a location (such as a LICENSE +file in a relevant directory) where a recipient would be likely to look +for such a notice. + +You may add additional accurate notices of copyright ownership. + +Exhibit B - "Incompatible With Secondary Licenses" Notice +--------------------------------------------------------- + + This Source Code Form is "Incompatible With Secondary Licenses", as + defined by the Mozilla Public License, v. 2.0. diff --git a/Readme.md b/Readme.md new file mode 100644 --- /dev/null +++ b/Readme.md @@ -0,0 +1,75 @@ +k8s-wrapper is a [wai](https://hackage.haskell.org/package/wai) application that is designed to wrap your service running in a k8s +environment and provide the additional functionality needed for a fully-featured application +to operate. It accomplishes it in several ways: + + 1. **Health and liveness Endpoints** — the feature provides information on the current state + of the application, allowing k8s to control execution, restart application, manage rollouts + and route traffic + 2. **Startup and Teardown Control** — the application's statup and teardown processes are managed + by `k8s-wrapper`, ensuring that your service operates smoothly + 3. **Graceful Shutdown Endpoint** — This feature enables graceful shutdown of your service. + 4. **Metrics Enpoint** — Metrics are exposed on a dedicated endpoint, allowing for easy monitoring + of your application's performance + +By utilizing k8s-wrapper, you can simplify the management of your service and ensure that it runs +reliably in a k8s environment + +# Get Started + +In order to use k8s application you should do: + +1. All k8s-wrapper to the list of dependencies in the cabal file: + +```cabal +executable mega-service + build-depends: base >= 4.4, + k8s-wrapper, + ... + ... +``` + +2. In the main file use: + +```haskell +import Network.K8s.Application as K8s + +main :: IO () +main = do + let runReadynessCheck = do + -- In this function we check if the traffic can be routed to the + -- application. If this function returns False traffic will not + -- be routed to the application. + pure True + let runLivenessCheck = do + -- Check if the application is in a workable state. If returns `False` + -- then k8s based on it's rules may restart the application. + pure True + let initializeServer = do + -- This function is used to initialize the service, for example + -- setup connection to the databases, check config files, register metrics + _ <- register ghcMetrics + -- While this function is executing k8s-wrapper replies the + -- status on it's interface. + + -- This function returns created resources that may be needed for the + -- application. + pure () + withK8sEndpoint + K8s.defConfig -- Default configuration + K8sChecks{ runReadynessCheck, runLivenessCheck } + initializeServer + (\resources -> Warp.run application_port (yourApp resources)) +``` + +After settings k8s-wrapper will start the interface on the port 10120 (can be redefinen in the config), +that provides endpoints: + + - **/started** — provides information if application is started + - **/ready** — provides information if application can accept the traffic + - **/health** — provides information if application is healthy + - **/stop** — preStop hook — requests application teardown + - `/_metrics` - output metrics for the application + +For the machine readable format you can check `spec.yaml` file provided with the package +that provides openapi v3 definition of the endpoints. + diff --git a/k8s-wrapper.cabal b/k8s-wrapper.cabal new file mode 100644 --- /dev/null +++ b/k8s-wrapper.cabal @@ -0,0 +1,67 @@ +cabal-version: 2.4 +name: k8s-wrapper +version: 0.1.0.0 +synopsis: Application wrapper for the k8s environment +description: A wrapper for the k8s environment. It provides the logic that + can automate the communication with k8s and easily provide proper + run in the application. + + For more details see documentation in the "Network.K8s.Application" + module + +homepage: https://github.com/cheopslab/k8s-wrapper + +bug-reports: https://github.com/cheopslab/k8s-wrapper/issues +license: MPL-2.0 +license-file: LICENSE +author: Alexander Vershilov +maintainer: alexander.vershilov@sirius.online, backend-dev@sirius.online +category: Network +extra-source-files: + CHANGELOG.md + spec.yaml + Readme.md +tested-with: GHC==9.2.2, GHC==9.0.2, GHC==8.10.7 + +library + exposed-modules: + Network.K8s.Application + default-extensions: + ImportQualifiedPost + LambdaCase + NumericUnderscores + OverloadedStrings + RecordWildCards + ScopedTypeVariables + build-depends: + base >=4.14.3.0 && <5.0, + async ^>= 2.2.4, + stm >=2.4 && <3.0, + text ^>=1.2.4.1, + http-types ^>=0.12.3, + wai, + wai-middleware-prometheus, + warp + hs-source-dirs: src + default-language: Haskell2010 + ghc-options: -Wall -Wextra + +test-suite k8s-wrapper-test + default-language: Haskell2010 + type: exitcode-stdio-1.0 + hs-source-dirs: test + default-extensions: + ImportQualifiedPost + main-is: unit.hs + ghc-options: -threaded + build-depends: + base >=4.14.3.0 && <5.0, + async ^>=2.2.4, + stm >=2.4 && <3.0, + text ^>=1.2.4.1, + tasty ^>=1.4.2.1, + tasty-hunit ^>=0.10.0.3, + lens ^>=5.1, + k8s-wrapper, + http-client, + http-types diff --git a/spec.yaml b/spec.yaml new file mode 100644 --- /dev/null +++ b/spec.yaml @@ -0,0 +1,124 @@ +openapi: 3.0.3 +info: + title: Management control interface + description: Service management interface + version: 0.0.1 +paths: + /started: + get: + summary: Application startup state. + description: |- + Returns information if the application is already started or not. + responses: + '200': + description: Application is in an operating state + content: + text/plain: + schema: + oneOf: + - $ref: "#/components/schemas/Ok" + - $ref: "#/components/schemas/TearingDown" + '400': + description: Application is in a starting state + content: + text/plain: + schema: + oneOf: + - $ref: "#/components/schemas/Starting" + + /ready: + get: + summary: Application readiness state. + description: |- + Tells if the k8s can route the traffic to this application. K8s periodically checks this + endpoint in order to understand if it can route traffic there. + responses: + '200': + description: Application is in an operating state + content: + text/plain: + schema: + oneOf: + - $ref: "#/components/schemas/Running" + '400': + description: Application is in a starting state + content: + text/plain: + schema: + oneOf: + - $ref: "#/components/schemas/Starting" + - $ref: "#/components/schemas/NotRunning" + - $ref: "#/components/schemas/TearingDown" + /health: + get: + summary: Application liveness state. + description: |- + Tells if the application is alive, if not k8s can restart this instance. + responses: + '200': + description: Application is in an operating state + content: + text/plain: + schema: + oneOf: + - $ref: "#/components/schemas/Running" + '400': + description: Application is in a starting state + content: + text/plain: + schema: + oneOf: + - $ref: "#/components/schemas/Starting" + - $ref: "#/components/schemas/Unhealthy" + /stop: + get: + summary: Request application teardown. + description: |- + Tells if to gracefully teardown, after being called the ready endpoint starts returning 400, + and no new traffic is accepted. All current requestes are processed. + + If users' appliction does not exit withing allowed timeout it's killed forcefully. + responses: + '200': + description: Application has accepted the teardown request + content: + text/plain: + schema: + oneOf: + - $ref: "#/components/schemas/TearingDown" + /_metrics: + get: + summary: Output metrics in prometheus format + description: |- + Output all the metrics provided by the application + responses: + '200': + description: Metrics for the application + content: + text/plain: + schema: + type: string + +components: + schemas: + Ok: + type: string + enum: ["ok"] + description: Application is working + Running: + type: string + enum: ["running"] + description: Application is running + NotRunning: + type: string + enum: ["not running"] + description: Application is not running + TearingDown: + enum: ["tearing down"] + description: Application is tearing down + Starting: + enum: ["starting"] + description: Application is starting + Unhealthy: + enum: ["unhealthy"] + description: Application is unhealthy diff --git a/src/Network/K8s/Application.hs b/src/Network/K8s/Application.hs new file mode 100644 --- /dev/null +++ b/src/Network/K8s/Application.hs @@ -0,0 +1,326 @@ +-- | +-- = k8s-wrapper +-- +-- The k8s Wrapper is a module designed to provide an interface for running +-- applications in the Kubernetes system. This wrapper spawns the server on an +-- internal protocol, providing endpoints for startup, liveness, and +-- readiness checks, as well as optional metrics support. +-- +-- There are some restrictions to be aware of when using this module. +-- First, the **server must be running in the main thread** in order to exit properly. +-- If this guarantee is not met, application and k8s will still function, but rollout +-- update procedures may take much longer. +-- +-- Second, the user's application must be able to tear down upon receiving +-- `AsyncCancelled` or `ThreadKilled` signals. While it's acceptable to implement +-- graceful teardowns, these should be time-bound. In general, applications that use +-- Warp handles this automatically. +-- +-- To use the k8s Wrapper, include the following configuration snippet in your pod: +-- +-- == __pod.yaml__ +-- @ +-- ... +-- spec: +-- metadata: +-- annotations: +-- prometheus.io/port: "9121" +-- prometheus.io/scrape: "true" +-- prometheus.io\/path: "\/_metrics" +-- containers: +-- - lifecycle: +-- preStop: +-- httpGet: +-- path: /stop +-- port: ${config.port} +-- # Period when after which the pod will be terminated +-- # even if the stop hook has not returned. +-- terminationGracePeriodSeconds: 30 +-- # When the service is considered started +-- # if the startup probe will not return success in +-- # `initialDealySeconds + periodSeconds * failureThreshold` seconds +-- # the service will be restarted +-- startupProbe: +-- httpGet: +-- path: /ready +-- port: ${config.port} +-- failureThreshold: 12 +-- initialDelaySeconds: 1 +-- periodSeconds: 5 +-- successThreshold: 1 +-- timeoutSeconds: 2 +-- # When the service is considered alive, if it's not alive it will be +-- # restarted according to it's policy +-- # initialDealySeconds + periodSeconds * failureThreshold +-- livenessProbe: +-- httpGet: +-- path: /health +-- port: ${config.health} +-- failureThreshold: 2 +-- initialDelaySeconds: 1 +-- periodSeconds: 10 +-- successThreshold: 1 +-- timeoutSeconds: 2 +-- readinessProbe: +-- httpGet: +-- path: /ready +-- port:${config.port} +-- failureThreshold: 2 +-- initialDelaySeconds: 1 +-- periodSeconds: 10 +-- successThreshold: 1 +-- timeoutSeconds: 2 +-- @ +-- +module Network.K8s.Application + ( withK8sEndpoint + , Config(..) + , defConfig + -- * Checks + -- $k8s-checks + , K8sChecks(..) + ) where + +import Control.Concurrent (killThread, threadDelay, forkIO) +import Control.Concurrent.Async +import Control.Concurrent.STM +import Control.Exception (finally, AsyncException, throwIO, fromException) +import Control.Monad +import Data.Foldable +import Network.HTTP.Types +import Network.Wai as Wai +import Network.Wai.Handler.Warp qualified as Warp +import Network.Wai.Middleware.Prometheus as Prometheus + +-- | Server configuration. +data Config = Config + { port :: Int -- ^ Port where control interface is statred. + , maxTearDownPeriodSeconds :: Int -- ^ How much time to wait before forceful teardown. + } deriving (Show) + +-- | Default configuration variables. +defConfig :: Config +defConfig = Config 10120 30 + +-- $k8s-checks +-- +-- There are two types of health checks that can be used: +-- +-- 1. __Deep check__ - this verifies not only basic startup but also that the services +-- the application communicates with are up and running. It is more precise, but it increases +-- the risk of marking services as unavailable and causing cascading errors. Therefore, +-- it is recommended to use deep checks for the `startupCheck`, but use shallow checks for the `livenessCheck`. +-- As for the `readinessCheck`, it is up to the user to decide which type of check to use. +-- 2. __Shallow check__ - this provides only the basic tests to ensure the application is running. +-- +-- The suggested approach for implementing the health checks is as follows: +-- +-- 1. The `startupCheck` should return @True@ after the server is started, configs were checked, +-- and communication with other services was established. Once it has returned @True@, the +-- function should always return @True@. +-- 2. The `readinessCheck` should return @True@ after the startup check has passed and after +-- population of the caches, preparing of the internal structures, etc. The function may +-- switch back to @False@ if the structures need repopulation and the application +-- can't serve the users. It's important to ensure that all the services in the cluster will +-- not switch to not ready state at the same time to avoid cascading failures. +-- 3. The `livenessCheck` performs a shallow check of the service and returns the state accordingly. +-- Generally, the `livenessCheck` should return @False@ only in the case where the server needs to be restarted. + +-- | Callbacks that the wrapper can use in order to understand the state of +-- the application and react accordingly. +data K8sChecks = K8sChecks + { runReadynessCheck :: IO Bool -- ^ Checks that application can receive requests + , runLivenessCheck :: IO Bool -- ^ Checks that application running (should not be restarted) + } + +-- | Application state. +data ApplicationState + = ApplicationStarting (Async ()) + | ApplicationRunning + | ApplicationTeardownConfirm (TVar Bool) + | ApplicationTearingDown + + +-- | Wrap a server that allows controlling business logic server. +-- The server can be communicated by the k8s services and can monitor the application livecycle. +-- +-- In the application run the following logic: +-- +-- @ +-- k8s_wrapper_server user code +-- +----------------+ +-- ready=false | initialization | +-- started=false | | +-- alive=false +----------------+ +-- | +-- started=true <-------------------+ +-- | +-- +---------------+ +-- | start server | +-- +---------------+ +-- | +-- ready? ---> check user thread, run callback +-- alive? ---> check user thread, run callback +-- @ +-- +-- +-- The server wrapper also provides additional logic: +-- 1. When checking liveness, the code checks if the thread running the server is still +-- alive and returns @False@ if it is not, regardless of what liveness check returns. +-- 2. When the `stop` action is called, the server starts to return @False@ in the readiness check. +-- Once it is asked by the server, it sends an Exception to the client code. +-- This ensures that no new requests will be sent to the server. +-- +-- In case of an asynchronous exception, we expect that we want to terminate the program. +-- Thus, we want to ensure a similar set of actions as a call to the @/stop@ hook: +-- +-- 1. Put the application in the tearing down state. +-- 2. Start replying with @ready=False@ replies. +-- 3. Once we replied with @ready=false@ at least once (or after a timeout), we trigger server stop. +-- In this place, we expect the server to stop accepting new connections and exit once all +-- current connections will be processed. This is the responsibility of the function provided by the user, +-- but servers like Warp already handle that properly. +-- +-- In case of an exception in the initialization function, it will be rethrown, and the function will exit with the same exception. +-- The k8s endpoint will be torn down. +-- +-- In case if the user code exists with an exception, it will be rethrown. Otherwise, the code exits properly. +withK8sEndpoint + :: Config -- ^ Static configuration of the endpoint. + -> K8sChecks -- ^ K8s hooks + -> IO a -- ^ Initialization procedure + -> (a -> IO b) -- ^ User supplied logic, see requirements for the server to work properly. + -> IO () +withK8sEndpoint Config{..} k8s startup action = do + startup_handle <- async startup + state_box <- atomically $ newTVar $ ApplicationStarting (fmap (const ()) startup_handle) + -- We start the server in the background, this is done synchronously + -- with running initialization procedure. + withAsync (do + x <- wait startup_handle + atomically (switchToRunning state_box) + action x) $ \server -> do + k8s_server <- async $ runK8sServiceEndpoint port maxTearDownPeriodSeconds k8s state_box server + (do result <- atomically $ asum + [ fmap void $ waitCatchSTM server + , readTVar state_box >>= \case + ApplicationTearingDown -> pure $ Right () + _ -> retry + ] + case result of + Left se + | Just (_ :: AsyncCancelled) <- fromException se -> pure () + | Just (_ :: AsyncException) <- fromException se -> pure () + | otherwise -> throwIO se + Right{} -> pure () + ) `finally` + (let half_interval = maxTearDownPeriodSeconds * 1_000_000 `div` 2 + in race_ (threadDelay half_interval) (cancel server)) + `finally` + (forkIO (cancel k8s_server)) + +-- | Run server with k8s endpoint. +-- +-- This endpoint provides k8s hooks: +-- 1. start +-- 2. liveness +-- 3. readyness +-- 4. pre_stop handler +-- +-- All other endpoints returns 404. +runK8sServiceEndpoint + :: Int -- ^ Port + -> Int -- ^ Shutdown interval + -> K8sChecks -- ^ K8s hooks + -> TVar ApplicationState -- ^ Projection of the application state + -> Async void -- ^ Handle of the running user code + -> IO () +runK8sServiceEndpoint port teardown_time_seconds K8sChecks{..} state_box server = Warp.run port $ \req resp -> do + case Wai.pathInfo req of + ["started"] -> do + readTVarIO state_box >>= \case + ApplicationStarting{} -> + resp $ responseLBS status400 [(hContentType, "text/plain")] "starting" + ApplicationRunning{} -> + resp $ responseLBS status200 [(hContentType, "text/plain")] "ok" + _ -> + resp $ responseLBS status200 [(hContentType, "text/plain")] "tearing down" + ["ready"] -> do + readTVarIO state_box >>= \case + ApplicationStarting{} -> + resp $ responseLBS status400 [(hContentType, "text/plain")] "starting" + ApplicationRunning{} -> do + isReady <- runReadynessCheck + if isReady + then resp $ responseLBS status200 [(hContentType, "text/plain")] "running" + else resp $ responseLBS status400 [(hContentType, "text/plain")] "not running" + ApplicationTeardownConfirm confirmed -> do + atomically $ writeTVar confirmed True + resp $ responseLBS status400 [(hContentType, "text/plain")] "tearing down" + ApplicationTearingDown{} -> + resp $ responseLBS status400 [(hContentType, "text/plain")] "tearing down" + ["health"] -> do + readTVarIO state_box >>= \case + ApplicationStarting{} -> + resp $ responseLBS status400 [(hContentType, "text/plain")] "starting" + _ -> do + isAlive <- runLivenessCheck + -- TODO: is thread ok? + if isAlive + then resp $ responseLBS status200 [(hContentType, "text/plain")] "running" + else resp $ responseLBS status400 [(hContentType, "text/plain")] "unhealthy" + ["stop"] -> do + _ <- async $ do + d <- registerDelay (teardown_time_seconds * 1_000_000) + join $ atomically $ switchToTeardown d state_box + -- this is interruptible, and waits until user thread will receive an + -- exception, but does not wait for the tearing down. + killThread $ asyncThreadId server + resp $ responseLBS status200 [(hContentType, "text/plain")] "tearing down" + ["_metrics"] -> metricsApp req resp + -- If it's any other path then we simply return 404 + _ -> resp $ Wai.responseLBS status404 [(hContentType, "text/plain")] "Not found" + +-- | Switches the application to the tearing down state. +-- +-- In case if the application was running it injects the confirmation +-- variable that is switched when the k8s system has seen that the +-- application is not ready. +-- +-- Returns an action that once finished tells that the application +-- can be teared down. The action does not wait longer that max +-- timeout period +switchToTeardown :: TVar Bool -> TVar ApplicationState -> STM (IO ()) +switchToTeardown timeout state = readTVar state >>= \case + ApplicationStarting init_thread -> do + writeTVar state ApplicationTearingDown + pure $ cancel init_thread + ApplicationRunning{} -> do + confirmed <- newTVar False + writeTVar state $ ApplicationTeardownConfirm confirmed + pure $ do + atomically $ asum + [ readTVar confirmed >>= check + , readTVar timeout >>= check + ] + atomically $ writeTVar state ApplicationTearingDown + ApplicationTeardownConfirm confirmed -> do + pure $ do + atomically $ asum + [ readTVar confirmed >>= check + , readTVar timeout >>= check + ] + atomically $ writeTVar state ApplicationTearingDown + ApplicationTearingDown -> + pure $ pure () + + +-- | Switch the state to the running in case if it was started. +-- Otherwise this is a noop. +switchToRunning :: TVar ApplicationState -> STM () +switchToRunning state = readTVar state >>= \case + ApplicationStarting{} -> do + writeTVar state ApplicationRunning + ApplicationRunning{} -> pure () + ApplicationTeardownConfirm{} -> pure () + ApplicationTearingDown -> pure () diff --git a/test/unit.hs b/test/unit.hs new file mode 100644 --- /dev/null +++ b/test/unit.hs @@ -0,0 +1,140 @@ +{-# LANGUAGE OverloadedStrings #-} +module Main (main) where + +import Control.Lens +import Control.Concurrent +import Control.Concurrent.Async +import Control.Exception +import Control.Monad +import Data.IORef +import Test.Tasty +import Test.Tasty.HUnit +import Network.K8s.Application qualified as K8s +import Network.HTTP.Client +import Network.HTTP.Types + +main :: IO () +main = defaultMain tests + +isAlive, isReady, isStarted :: Manager -> IO Bool +isAlive manager = + let req = "http://localhost:10120/health" + in httpNoBody req manager <&> (==200) . statusCode . responseStatus +isReady manager = + let req = "http://localhost:10120/ready" + in httpNoBody req manager <&> (==200) . statusCode . responseStatus +isStarted manager = + let req = "http://localhost:10120/started" + in httpNoBody req manager <&> (==200) . statusCode . responseStatus +stopIt :: Manager -> IO () +stopIt manager = + let req = "http://localhost:10120/stop" + in void $ httpNoBody req manager + +tests :: TestTree +tests = testGroup "unit" + [ testGroup "startup" + [ testCaseSteps "Normal startup" $ \step -> do + manager <- newManager defaultManagerSettings + step "Preparing.." + lock <- newEmptyMVar + finished <- newEmptyMVar + closed <- newEmptyMVar + ready_var <- newIORef True + alive_var <- newIORef True + k8s <- async $ K8s.withK8sEndpoint + K8s.defConfig{K8s.maxTearDownPeriodSeconds=1} + K8s.K8sChecks + { K8s.runReadynessCheck = readIORef ready_var + , K8s.runLivenessCheck = readIORef alive_var + } + (takeMVar lock) + (\x -> putMVar finished x >> takeMVar closed) + assertBool "appication should not be started" . not =<< isStarted manager + assertBool "appication should not be ready" . not =<< isReady manager + assertBool "appication should not be alive" . not =<< isAlive manager + step "initialization has finished" + writeIORef ready_var False + writeIORef alive_var False + putMVar lock () >> yield + assertBool "appication should be started" =<< isStarted manager + assertBool "appication should not be ready" . not =<< isReady manager + assertBool "appication should not be alive" . not =<< isAlive manager + step "application is alive now" + writeIORef alive_var True + assertBool "appication should be started" =<< isStarted manager + assertBool "appication should not be ready" . not =<< isReady manager + assertBool "appication should be alive" =<< isAlive manager + writeIORef ready_var True + step "application is ready now" + assertBool "appication should be started" =<< isStarted manager + assertBool "appication should be ready" =<< isReady manager + assertBool "appication should be alive" =<< isAlive manager + step "teardown" + cancel k8s + , testCase "Exception on startup" $ do + e <- try $ K8s.withK8sEndpoint + K8s.defConfig{K8s.maxTearDownPeriodSeconds=1} + (K8s.K8sChecks (pure True) (pure True)) + (throwIO (userError "foo") :: IO ()) + (pure) + assertEqual "Should be exception" (Left (userError "foo")) e + , testCase "Exits on application exit" $ do + K8s.withK8sEndpoint + K8s.defConfig{K8s.maxTearDownPeriodSeconds=1} + (K8s.K8sChecks (pure True) (pure True)) (pure ()) + pure + ] + , testGroup "teardown" + [ testCaseSteps "Kills application after /stop and /ready" $ \step -> do + manager <- newManager defaultManagerSettings + lock <- newEmptyMVar + received_exception <- newIORef False + x <- async $ K8s.withK8sEndpoint + K8s.defConfig{K8s.maxTearDownPeriodSeconds=1} + (K8s.K8sChecks (pure True) (pure True)) + (pure ()) + (\() -> do + takeMVar lock `finally` (writeIORef received_exception True)) + step "Stopping the application" + stopIt manager + replicateM_ 100 yield -- Hack :( + step "Check that it's still running" + assertBool "should not receive exception" . not =<< readIORef received_exception + step "Check ready" + assertBool "appication should not be ready" . not =<< isReady manager + step "Check that application is closing" + assertBool "should receive exception" =<< readIORef received_exception + wait x + putMVar lock () + , testCaseSteps "Kills application after /stop and timeout" $ \step -> do + manager <- newManager defaultManagerSettings + lock <- newEmptyMVar + received_exception <- newIORef False + x <- async $ K8s.withK8sEndpoint + K8s.defConfig{K8s.maxTearDownPeriodSeconds=1} + (K8s.K8sChecks (pure True) (pure True)) + (pure ()) + (\() -> do + takeMVar lock `finally` (writeIORef received_exception True)) + step "Stopping the application" + stopIt manager + replicateM_ 100 yield -- Hack :( + step "Check that it's still running" + assertBool "should not receive exception" . not =<< readIORef received_exception + wait x + putMVar lock () + , testCase "Exits if application is terminating for too long" $ do + manager <- newManager defaultManagerSettings + lock <- newEmptyMVar + x <- async $ K8s.withK8sEndpoint + K8s.defConfig{K8s.maxTearDownPeriodSeconds=1} + (K8s.K8sChecks (pure True) (pure True)) + (pure ()) + (\() -> do + takeMVar lock `finally` (takeMVar lock)) + stopIt manager + wait x + putMVar lock () + ] + ]