How do I check that a docker host is in swarm mode? - docker

Question

After executing this;
eval $(docker-machine env mymachine)
How do I check if the docker daemon on mymachine is a swarm manager?

Answer 1

To check general swarm membership, my preferred method is to use the formatted output from docker info. The possible values of this are currently inactive, pending, active, locked, and error:
case "$(docker info --format '{{.Swarm.LocalNodeState}}')" in
inactive)
echo "Node is not in a swarm cluster";;
pending)
echo "Node is not in a swarm cluster";;
active)
echo "Node is in a swarm cluster";;
locked)
echo "Node is in a locked swarm cluster";;
error)
echo "Node is in an error state";;
*)
echo "Unknown state $(docker info --format '{{.Swarm.LocalNodeState}}')";;
esac
To check for manager status, rather than just a node in a cluster, the field you want is .Swarm.ControlAvailable:
docker info --format '{{.Swarm.ControlAvailable}}'
That will output "true" for managers, and "false" for any node that is a worker or not in a swarm.
To identify worker nodes, you can join to two:
if [ "$(docker info --format '{{.Swarm.LocalNodeState}}')" = "active" \
-a "$(docker info --format '{{.Swarm.ControlAvailable}}')" = "false" ]; then
echo "node is a worker"
else
echo "node is not a worker"
fi

Answer 2

You could also use docker info to see the result of Swarm property (inactive or active).
For example:
function isSwarmNode(){
if [ "$(docker info | grep Swarm | sed 's/Swarm: //g')" == "inactive" ]; then
echo false;
else
echo true;
fi
}

Answer 3

I don't have a swarm node handy at the moment, but it looks as if you could simply run something like docker node ls. When targeting a docker daemon that is not in swarm node, that results in:
Error response from daemon: This node is not a swarm manager. Use "docker swarm init" or "docker swarm join" to connect this node to swarm and try again.
And it returns a nonzero exit code
$ echo $?
1
So the test would look something like:
if docker node ls > /dev/null 2>&1; then
echo this is a swarm node
else
echo this is a standalone node
fi

Answer 4

In addition to larsks answer, if you run docker node ls when pointing to a worker node, you'll get the following message:
Error response from daemon: This node is not a swarm manager. Worker nodes can't be used to view or modify cluster state. Please run this command on a manager node or promote the current node to a manager.
You can use this to differentiate between worker nodes and nodes not in a swarm at all.

Answer 5

Make sure your docker environment variables are set properly
$env | grep DOCKER_
Compare url and port values with the output from
$docker-machine ls
Select the swarm master machine name and you can reset the environment variables using
$eval $(docker-machine env your_master_machine_name)
Once environment variables are set properly, your command
$docker info | egrep '^Swarm: ' | cut -d ' ' -f2
should give the correct result

Answer 6

To get the IP address of a manager from any node (either worker or manager) using bash you can do:
read manager_ip _ <<<$(IFS=':'; echo $(docker info --format "{{ (index .Swarm.RemoteManagers 0).Addr }}"))
echo "${manager_ip}"
As mentioned above, the most direct way to identify if the current node is a manager is by using:
docker info --format '{{.Swarm.ControlAvailable}}'