haproxy-consul-template
Alpine docker container hosting HAProxy with dynamic config updating through consul-template with process supervision using s6
About this image
This creates a small container with s6 supervisor running and monitoring HAProxy and consul-template. The container runs two instances of HAProxy in order to let us keep HAProxy's graceful restart while still having supervision of the process.
Why s6?
- We need to run more than one process inside the container
- Small, minimal footprint
- Secure and stable
You can read more about s6 here.
How to use this image
If you have good directory structure as such:
consul-template
│
└───config.d
│ └── consul-template.conf
│
└───templates
└── haproxy.ctmpl
then all you need to do is run the container with a bind mount on the consul-template directory:
docker run -d -v /path/to/consul-template/:/consul-template/ cavemandaveman/haproxy-consul-template:latest
Otherwise, you need a separate bind mount argument for your consul-template config and template files. However, the config must always live at /consul-template/config.d inside the container.
Also in the docker run command, include either as many -p port:port args as bind ports you have defined, or use --net=host. The former is recommended and is more secure.
In your consul-template.conf, you must include the following destination= and command= values in the template{} block in order to properly reload the HAProxy configuration:
template {
destination = "/etc/haproxy/haproxy.cfg"
command = "restart-haproxy"
}What does the the restart script do?
First, we tell the current HAProxy to not restart itself when killed, because by default s6 will keep restarting the process (like a good supervisor should). Next, we start the alternate instance of HAProxy (which in turn softly kills haproxy -db -f /etc/haproxy/haproxy.cfg -sf $(pidof haproxy) the old HAProxy instance). Then we change the links of the alternate instance to the current instance and vice versa in order for the next restart to work properly. You can read more about the idea directly from the creator of s6.