Docker Cookbook

312 | Chapter 10: Application Use Cases

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$ docker restart elb
$ curl http://192.168.33.10
a970ec6274ca
$ curl http://192.168.33.10
8eaab9c31e1a
$ curl http://192.168.33.10
71d8297c1538
The only thing left to do now is to run 
confd
in a daemon mode, and instruct it to
stop and restart the Nginx container when changes to the configuration are done. To
do this, edit 
/etc/confd/conf.d/config.toml
and add a 
reload_cmd
to restart Nginx like
so (this assumes you named your Nginx container 
elb
as indicated earlier):
[template]
src = "config.conf.tmpl"
dest = "/home/vagrant/nginx.conf"
keys = [
"/elb/hostname",
]
reload_cmd = "docker restart elb"
Finally, run 
confd
in daemon mode, and for testing, set a short interval for when it
will poll Consul. Then have fun starting and stopping your application container. You
will see that every time you start or stop/kill an application container, 
confd
will
dynamically update your configuration and restart the 
elb
container:
$ ./confd -backend consul -interval 5 -node 192.168.33.10:8500
... ./confd[1463]: WARNING Skipping confd config file.
... ./confd[1463]: INFO /home/vagrant/nginx.conf has md5sum \
acf6552d92cb9eb79b1068cf40b8ec0f should be 001894b713827404d0c5e72e2a66844d
... ./confd[1463]: INFO Target config /home/vagrant/nginx.conf out of sync
... ./confd[1463]: INFO Target config /home/vagrant/nginx.conf has been updated
... ./confd[1463]: INFO /home/vagrant/nginx.conf has md5sum \
001894b713827404d0c5e72e2a66844d should be cecb5ddc469ba3ef17f9861cde9d529a
... ./confd[1463]: INFO Target config /home/vagrant/nginx.conf out of sync
... ./confd[1463]: INFO Target config /home/vagrant/nginx.conf has been updated
... ./confd[1463]: INFO /home/vagrant/nginx.conf has md5sum \
cecb5ddc469ba3ef17f9861cde9d529a should be 0b97f157f437083ffba43f93a426d28f
... ./confd[1463]: INFO Target config /home/vagrant/nginx.conf out of sync
... ./confd[1463]: INFO Target config /home/vagrant/nginx.conf has been updated
This is dynamic load balancing with Docker. To make it elastic, you would need to
monitor the load and automatically start a new application container, which would
trigger a reconfiguration of the 
elb
configuration.
Discussion
This recipe is quite long and has many steps. To facilitate the testing, I prepared a
Vagrant box, as always; try this: