leader

Rancher Leader Election

This is very simple approach to leader election that uses Rancher Meta-data. Every container in a service is given a create_index that increments with each container that is launched in the service. The container with the lowest create_index will be chosen as the master.

Using

This binary is expected to be ran as an ENTRYPOINT to your container. For example

FROM service
ADD https://github.com/rancher/leader/releases/download/v0.1.0/leader /usr/bin/
RUN chmod +x /usr/bin/leader
ENTRYPOINT ["leader"]
CMD ["service", "args"]

On startup the leader binary will check metadata and see if this container is the leader. If it is the leader the arguments to leader will be executed. If the container is not the leader it will just wait until it becomes the leader (ie has the lowest create_index).

Port proxying

You can pass --proxy-tcp-port 8080 to the leader program and that will make all non-leader containers just forward traffic to port 8080 of the leader.

Embed in script

Additionally you can just run leader -check to check if this container is the leader or not. If it is the leader it will exit with status code 0, otherwise 1.

Usage

NAME:
   ./dist/artifacts/leader - Simple leader election with Rancher

USAGE:
   ./dist/artifacts/leader [global options] command [command options] [arguments...]
   
COMMANDS:
   help, h	Shows a list of commands or help for one command
   
GLOBAL OPTIONS:
   --proxy-tcp-port "0"		Port to proxy to the leader
   --check			Check if we are the leader and exit
   --help, -h			show help
   --generate-bash-completion	
   --version, -v		print the version

License

Copyright (c) 2014-2015 Rancher Labs, Inc.

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.