[Feature] LoadBalancer

Author: grachevko

README.md

@@ -60,4 +60,17 @@ $ docker run -d --label ru.grachevko.dhu="nginx.local:10" nginx
 $ ping nginx.local
 ```
 Container with greater priority will be used, by default priority is 0. 
-If priority are the same then early created container will be used.
+If priority are the same then early created container will be used.
+
+Load Balancer
+----
+In order to pass traffic through loadbalancer you can define container name which ip will be used to record in hosts. 
+Just add one more colon and container name after.
+```bash
+$ docker run -d --name lb nginx
+$ docker run -d --label ru.grachevko.dhu="nginx1.local:0:lb" nginx
+$ docker run -d --label ru.grachevko.dhu="nginx2.local:0:lb" nginx
+$ ping nginx1.local // ip of lb
+$ ping nginx2.local // ip of lb
+```
+Keep in mind, loadbalancer container must have fixed name.

docker-compose.yml

@@ -8,6 +8,11 @@ services:
         volumes:
             - /var/run/docker.sock:/var/run/docker.sock
             - ./:/usr/local/app
+            - /etc/hosts:/opt/hosts
+
+    lb:
+        image: nginx:alpine
+        container_name: lb
 
     nginx:
         image: nginx:alpine
@@ -23,3 +28,13 @@ services:
         image: nginx:alpine
         labels:
             ru.grachevko.dhu: 'img.nginx.local:3;api.nginx.local:5'
+
+    nginx4:
+        image: nginx:alpine
+        labels:
+            ru.grachevko.dhu: 'nginx4.local:0:lb'
+
+    nginx5:
+        image: nginx:alpine
+        labels:
+            ru.grachevko.dhu: 'nginx5.local:0:lb'

main.py

@@ -16,22 +16,30 @@ def scan():
     containers = []
     for container in docker.containers.list():
         label = container.attrs.get('Config').get('Labels').get(LABEL)
-        if label:
-            ip = next(iter(container.attrs.get('NetworkSettings').get('Networks').values())).get('IPAddress')
+        if not label:
+            continue
+
+        for string in label.split(';'):
+            priority = 0
+            lb = container
+
+            if ':' in string:
+                parts = string.split(':')
+                string = parts[0]
+                priority = int(parts[1]) if len(parts) >= 2 else priority
+                lb = docker.containers.get(parts[2]) if len(parts) == 3 else lb
+
+            if not lb:
+                continue
+
+            ip = next(iter(lb.attrs.get('NetworkSettings').get('Networks').values())).get('IPAddress')
             if ip:
-                for string in label.split(';'):
-                    if ':' in string:
-                        string, priority = string.split(':')
-                        priority = int(priority)
-                    else:
-                        priority = 0
-
-                    containers.append({
-                        'ip': ip,
-                        'priority': priority,
-                        'hosts': string_to_array(string),
-                        'createdAt': container.attrs.get('Created')
-                    })
+                containers.append({
+                    'ip': ip,
+                    'priority': priority,
+                    'hosts': string_to_array(string),
+                    'createdAt': container.attrs.get('Created'),
+                })
 
     return containers