Serf on Docker

This is a docker image and a couple of helper bash function, to work with serf.

This document describe the process:

• create the docker image
• start a cluster of connected serf agent running in docker containers
• stop/start nodes to check how membership gossip works

Create the image

git clone git@github.com:sequenceiq/docker-serf.git
cd docker-serf
git checkout serf-only
docker build -t sequenceiq/serf .

start a demo cluster

run 3 docker container from the image you just built. all of them is running in the background (-d docker parameter)

• serf0 the first one doesn't joins to a cluster as he is the first
• serf<1..n> nodes connecting to the cluster

serf-start-cluster function defaults to starting 3 nodes. if you want more just add a parameter serf-start-cluster 5

# load helper bash functions serf-xxx
. serf-functions

# start a cluster with 3 nodes
serf-start-cluster

# check the running nodes
docker ps

start a test node and attach

it starts a new container name serf99, but not in the brackound, like the previous ones. you will be attached to the container, which:

• joins the cluster
• starts a /bin/bash ready to use

serf-test-instance

# once attached to the test instance prompt changes to [bash-4.1#]
serf members

you will see now all memebers including the test instance itself serf99

serf99.mycorp.kom  172.17.0.5:7946  alive  
serf1.mycorp.kom   172.17.0.3:7946  alive  
serf0.mycorp.kom   172.17.0.2:7946  alive  
serf2.mycorp.kom   172.17.0.4:7946  alive

Start/stop a node

Stop one of the nodes:

docker stop -t 0 serf1

now if you run again the serf members in serf99 you will notice serf1 node marked as failed. note: it might take a couple of seconds, until the cluster gossips around the failure of node99.

serf99.mycorp.kom  172.17.0.5:7946  alive
serf1.mycorp.kom   172.17.0.3:7946  failed  
serf0.mycorp.kom   172.17.0.2:7946  alive
serf2.mycorp.kom   172.17.0.4:7946  alive

if you resart the node serf1:

docker start serf1

It will apear again as live. Check it on serf99:

serf members

serf99.mycorp.kom  172.17.0.5:7946  alive  
serf1.mycorp.kom   172.17.0.3:7946  alive  
serf0.mycorp.kom   172.17.0.2:7946  alive  
serf2.mycorp.kom   172.17.0.4:7946  alive