A small demo to run two nginx containers in active-passive mode by using keepalived and VIP.
This demo is made to simulate a scenario with two running nginx servers, one as a master and another as a backup, in order to achieve high availability.
There are some limitations in this demo:
- I run it in a single host. Normally, it would be better to create a scenario with two hosts.
- I didn't spend time to map the virtual IP from docker network to the host. Instead, I use a haproxy to do this task.
- Running both nginx and keepalived in an Alpine container is not easy. rc-service could not manage keepalived properly. I thought to use supervisor or circus, but they are a bit heavy in space. So I directly run keepalived as a background daemon. However, the drawback is if it fails, it will not restart (not robust).
Run the following command:
$ docker-compose up -dNow, visit localhost:8000 and you would see Primary.
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
42cc6637255b nginxkeepaliveddockerdemo_nginx_slave "/entrypoint.sh" 28 seconds ago Up 24 seconds 80/tcp nginxkeepaliveddockerdemo_nginx_slave_1
3f39a7e356ce haproxy:1.7-alpine "/docker-entrypoin..." 28 seconds ago Up 25 seconds 0.0.0.0:8000->6301/tcp nginxkeepaliveddockerdemo_proxy_1
6151af0d50db nginxkeepaliveddockerdemo_nginx_master "/entrypoint.sh" 28 seconds ago Up 24 seconds 80/tcp nginxkeepaliveddockerdemo_nginx_master_1Try to pause the master server:
$ docker pause nginxkeepaliveddockerdemo_nginx_master_1Now, visit localhost:8000 and you should see Secondary.
Recover the master server and pause the slave server:
$ docker unpause nginxkeepaliveddockerdemo_nginx_master_1
$ docker pause nginxkeepaliveddockerdemo_nginx_slave_1Visit localhost:8000 and you should see Primary again.
As you can see, when a master server is down, a backup server does automatic failover.