Docker Glue

Automated unattended pluggable docker management based on docker events.
Can be used to update load-balancers, DNS, service discovery, …etc.
Managing docker containers would be as simple as tagging them with some labels

Use Cases

• Dynamically add/remove containers to/from load-balancer (currently haproxy using jinja2 templates)
• can send traffic of a specific domain to corresponding containers based on Host HTTP header
• can send traffic of a specific path prefix to corresponding containers
• Replace docker0 bridge,docker-proxy, …etc with more advanced SDN (like OVS or OpenStack Neutron).
• Run a specific handler code (python plugins) or handler script based on docker events
• publish containers inspection to discovery service (like etcd)

Daemons

• docker-glue the modular pluggable daemon that can run handlers and scripts
• docker-balancer a standalone daemon that just updates haproxy (a special case of glue)

You can pass -1 to run once, and -w to wait for events, and -h for details.

Requirements and Installation

yum install haproxy python-docker-py python-jinja2
cp docker-balancer.service /etc/systemd/system/docker-balancer.service
cp docker-glue.service /etc/systemd/system/docker-glue.service

Using Docker Balancer

you can set labels like (replace 80 with any port):

• glue_http_80_host the HTTP host to which this container would be attached in the load-balancer
• glue_http_80_prefix the prefix (without leading /) to attach it to
• glue_http_80_strip_prefix pass 1 if the prefix should be stripped before passing to backend
• glue_http_80_weight the weight (defaults to 100)

let’s assume that you have started docker-balancer -w or the docker-balancer service

docker run -d --name wp1 -l glue_http_80_host='wp1.example.com' mywordpress/wordpress 
docker run -d --name wp2 -l glue_http_80_host='wp2.example.com' mywordpress/wordpress 
docker run -d --name os-ui1 -l glue_http_80_host=openstack.example.com -l glue_http_80_prefix=dashboard/horizon myopenstack/horizon
docker run -d --name os-id1 -l glue_http_80_host=openstack.example.com -l glue_http_80_prefix=identity/keystone myopenstack/keystone

Using Docker Glue

in docker-glue.d you have many .example files copy the files you need to remove that extension, for example

cd docker-glue.d
cp lb.ini.example lb.ini
cp test.ini.example test.ini
cd ..

then start docker-glue daemon or run docker-glue -w

Handlers INI files

files in docker-glue.d/*.ini (we have included examples) looks like this

[handler]
class=DockerGlue.handlers.exec.ScriptHandler
events=all
enabled=1
triggers-none=0
[params]
script=test-handler.sh
demo-option=some value

handler section specifies what and when to run

• class the handler plugin, which can be one of
  • DockerGlue.handlers.exec.ScriptHandler executes a shell script
    • test-handler.sh a demo script that logs the event to /tmp/docker-glue-test.log
    • ovs-handler.sh connect the container to OpenVSwicth
  • DockerGlue.handlers.lb.HAProxyHandler load balancer that uses HAProxy
  • DockerGlue.handlers.publishers.distconfig.Publisher publish containers to discovery service like etcd
• events the even statuses (comma separated) that triggers this handler, can be none (which is dummy event) or all (which does not include none)
• enabled
• triggers-none - set it if you want this handler to triggers none dummy event

params section is custom params to be passed to the handler

Writing script plugins

scripts in handler-scripts will be passed the ini path and docker event and the docker container id for example it might be like this test-handler.sh test.ini start 123456

the code of test-handler.sh look like this

#! /bin/bash
cd `dirname $0`
function error() {
    echo "$@"
    exit -1
}
[ $# -ne 3 ] && error "Usage `basename $0` config.ini status container_id"
ini="$1"
status="$2"
container_id="$3"
ini_demo_option=$( crudini --inplace --get $ini params demo-option 2>/dev/null || : )
echo "`date +%F` container_id=[$container_id] status=[$status] ini_demo_option=[$ini_demo_option]" >> /tmp/docker-glue-test.log

as you can see you can read options using crudini from the passed ini file.

Writing python plugins

just extend BaseHandler and in the __init__ do what ever you need, and read your custom params from the ini and implement a handle method like this

from . import BaseHandler
logger = logging.getLogger(__name__)
class DemoHandler(BaseHandler):
    def __init__(self, agent, ini_file, ini):
        BaseHandler.__init__(self, agent, ini_file, ini)
        self.custom_param=ini.get('params', 'custom_param') if ini.has_option('params', 'custom_param') else None
    def handle(self, event, container_id):
        logger.info('got event=%r on container=%r and custom_param=%r', event, container_id, self.custom_param)

TODO

• implement TCP/UDP load balancing using ipvsadm or keepalived