feat: container filters environment variable

Author: buchdag

README.md

@@ -156,6 +156,8 @@ Environment Variables:
   DOCKER_HOST - default value for -endpoint
   DOCKER_CERT_PATH - directory path containing key.pem, cert.pem and ca.pem
   DOCKER_TLS_VERIFY - enable client TLS verification
+  DOCKER_CONTAINER_FILTERS - comma separated list of container filters for inclusion by docker-gen.
+    Filters supplied through this variable override filters supplied through the -container-filter options.
 ```
 
 If no `<dest>` file is specified, the output is sent to stdout. Mainly useful for debugging.

cmd/docker-gen/main.go

@@ -86,6 +86,8 @@ Environment Variables:
   DOCKER_HOST - default value for -endpoint
   DOCKER_CERT_PATH - directory path containing key.pem, cert.pem and ca.pem
   DOCKER_TLS_VERIFY - enable client TLS verification
+  DOCKER_CONTAINER_FILTERS - comma separated list of container filters for inclusion by docker-gen.
+    Filters supplied through this variable override filters supplied through the -container-filter options.
 `)
 	println(`For more information, see https://github.com/nginx-proxy/docker-gen`)
 }
@@ -121,6 +123,13 @@ func initFlags() {
 		"include stopped containers. Bypassed when providing a container status filter (-container-filter status=foo).")
 	flag.Var(&containerFilter, "container-filter",
 		"container filter for inclusion by docker-gen. You can pass this option multiple times to combine filters with AND. https://docs.docker.com/engine/reference/commandline/ps/#filter")
+	// override containerFilter with DOCKER_CONTAINER_FILTERS environment variable
+	if filters := strings.Split(os.Getenv("DOCKER_CONTAINER_FILTERS"), ","); len(filters) > 0 && filters[0] != "" {
+		containerFilter = make(mapstringslice)
+		for _, filter := range filters {
+			containerFilter.Set(filter)
+		}
+	}
 
 	// Command notification options
 	flag.StringVar(&notifyCmd, "notify", "", "run command after template is regenerated (e.g `restart xyz`)")