# legion-discovery-client
This is a Haskell client library used to communicate with the Legion
Discovery discovery service.
## Performing a query without registering a service.
If you want to perform a query without registering yourself a service,
the following example is how you might typically accomplish that. Note
that even though you are not starting a service, you must still specify
a name and a version for the local program. The reason for this is
that Legion Discovery keeps track of all requests in order to build a
dependency graph of your service ecosystem.
```haskell
import Network.HTTP.Client as C
import OM.Discovery (connect, query)
...
let
name = "my-program" {- the name of this client program. -}
version = "0.1" {- the version of this client program. -}
targetService = "some-service" {- the name of the service you are looking for. -}
targetRange = "> 1.1.1 && < 1.2" {- the range of acceptable versions you wish to find. -}
in do
manager <- C.newManager C.defaultManagerSettings
discovery <- connect name version manager
servicesInstances <- query targetService targetRange discovery
...
```
## Registering a service.
The following example shows how to register a service, using
`withService`.
```haskell
import Network.HTTP.Client as C
import OM.Discovery (connect, withService)
...
let
name = "my-program" {- the name of this client program. -}
version = "0.1" {- the version of this client program. -}
serviceAddr = "http://ec2-foo-bar.amazon.com:8080" {- the address on which your service is running. -}
in do
manager <- C.newManager C.defaultManagerSettings
discovery <- connect name version manager
withService serviceAddr discovery $ do
{-
Your service code here. When this IO block exits (for any reason,
including exceptions) then the service will unregister itself.
-}
```