Merge pull request #5 from Clever/INFRA-1563-update-documentation

Updated README.

Author: xavi-

README.md

@@ -1,8 +1,8 @@
 # discovery-python
 
-Programmatically find service endpoints.
+This library programmatically finds endpoints for dependencies. Similar to [discovery-go](https://github.com/Clever/discovery-go) and [disocvery-node](https://github.com/Clever/discovery-node).
 
-This library currently is just an abstraction around reading environment variables used for dependent services.
+See [Service Discovery](https://github.com/Clever/infra-docs/blob/master/deploy/service_discovery.md) for more details.
 
 ## Installation
 
@@ -55,21 +55,6 @@ except discovery.MissingEnvironmentVariableError as e:
 
 ```
 
-## Environment Variables
-
-This library currently requires environment variables to be defined in the following format:
-
-```
-SERVICE_{SERVICE_NAME}_{EXPOSE}_{PROTO|HOST|PORT}
-```
-
-### Example:
-```bash
-SERVICE_STOKED_THRIFT_PROTO = "tcp"
-SERVICE_STOKED_THRIFT_HOST = "localhost"
-SERVICE_STOKED_THRIFT_PORT = "90"
-```
-
 ## Development
 
 ### Publishing a new version
@@ -82,3 +67,21 @@ SERVICE_STOKED_THRIFT_PORT = "90"
     ```sh
     ./publish.sh
     ```
+
+### Implementation Details
+
+Currently, `discovery-{go,node,python}` looks for environment variables with the following format:
+
+```
+SERVICE_{SERVICE_NAME}_{EXPOSE_NAME}_{PROTO,HOST,PORT}
+```
+
+These environment variables are autogenerated by [fab](http://github.com/Clever/fabulaws) and [catapult](http://github.com/Clever/catapult) during app deployment.  Three env-vars are created for each app listed in the `dependencies` section of caller's launch yaml.
+
+For example, if an app lists `district-authorizations` as a dependency, fab and catapult will generate this env-vars triplet:
+
+```bash
+SERVICE_DISTRICT_AUTHORIZATIONS_HTTP_PROTO = "http"
+SERVICE_DISTRICT_AUTHORIZATIONS_HTTP_HOST = "district-authorizations.ops.clever.com"
+SERVICE_DISTRICT_AUTHORIZATIONS_HTTP_PORT = "80"
+```