Merge pull request #46 from dgilling/patch-1

Update README.rd, Add missing information on ADDITONAL_SERVICES for S…

Author: Feng Honglin

README.md

@@ -76,7 +76,7 @@ Legacy link refers to the link created before docker 1.10, and the link created
 **Note**: Any link alias sharing the same prefix and followed by "-/_" with an integer is considered to be from the same service. For example: `web-1` and `web-2` belong to service `web`, `app_1` and `app_2` are from service `app`, but `app1` and `web2` are from different services.
 
 
-### Running with Docker Compose v2(new links, compatible with Docker Swarm)
+### Running with Docker Compose v2(new links)
 
 Docker Compose 1.6 supports a new format of the compose file. In the new version(v2), the old link that injects environment variables is deprecated.
 
@@ -86,7 +86,6 @@ Similar to using legacy links, here list some differences that you need to notic
 - A link is required in order to ensure that dockercloud/haproxy is aware of which service it needs to balance, although links are not needed for service discovery since docker 1.10. Linked aliases are not required.
 - DO not overwrite `HOSTNAME` environment variable in `dockercloud/haproxy container`.
 - As it is the case on Docker Cloud, auto reconfiguration is supported when the linked services scales or/and the linked container starts/stops.
-- This image is also compatible with Docker Swarm, and supports the docker native `overlay` network across multi-hosts.
 
 ##### example of docker-compose.yml running in linux:
 
@@ -124,6 +123,41 @@ Similar to using legacy links, here list some differences that you need to notic
 
 Once the stack is up, you can scale the web service using `docker-compose scale web=3`. dockercloud/haproxy will automatically reload its configuration.
 
+#### Running with Docker Compose v2 and Swarm (using envvar)
+When using links like previous section, the Docker Swarm scheduler can be too restrictive. 
+Even with overlay network, swarm (As of 1.1.0) will attempt to schedule haproxy on the same node as the linked service due to legacy links behavior. 
+This can cause unwanted scheduling patterns or errors such as "Unable to find a node fulfilling all dependencies..."
+
+Since Compose V2 allows discovery through the service names, Dockercloud haproxy only needs the links to indentify which service should be load balanced.
+
+A second option is to use the `ADDITIONAL_SERVICES` variable for indentification of services.
+
+- Set the `ADDITIONAL_SERVICES` env variable to your linked services.
+- You also want to set depends_on to ensure the web service is started before haproxy so that the hostname can be resolved. This controls scheduling order but not location.
+- The container still needs access to the docker daemon to get load balanced containers' configs.
+- If any trouble with haproxy not updating the config, try running reload.sh or set the `DEBUG` envvar.
+- This image is also compatible with Docker Swarm, and supports the docker native `overlay` network across multi-hosts.
+
+##### example of docker-compose.yml in 'project_dir' directory running in linux:
+
+	version: '2'
+	services:
+	  web:
+	    image: dockercloud/hello-world
+	  blog:
+	    image: dockercloud/hello-world
+	  lb:
+	    image: dockercloud/haproxy
+    	   depends_on:
+             - web
+             - blog
+           environment:
+             - ADDITIONAL_SERVICES=project_dir:web,project_dir:blog
+	    volumes:
+	      - /var/run/docker.sock:/var/run/docker.sock
+	    ports:
+	      - 80:80
+
 ## Configuration
 
 ### Global and default settings of HAProxy###