page_title	page_description	page_keywords
Docker Swarm discovery	Swarm discovery	docker, swarm, clustering, discovery

Discovery

Docker Swarm comes with multiple Discovery backends.

Backends

You use a hosted discovery service with Docker Swarm. The service maintains a list of IPs in your swam. There are several available services, such as etcd, consul and zookeeper depending on what is best suited for your environment. You can even use a static file. Docker Hub also provides a hosted discovery service which you can use.

Hosted Discovery with Docker Hub

This example uses the hosted discovery service on Docker Hub. Using Docker Hub's hosted discovery service requires that each node in the swarm is connected to the internet. To create your swarm:

First we create a cluster.

# create a cluster
$ swarm create
6856663cdefdec325839a4b7e1de38e8 # <- this is your unique <cluster_id>

Then we create each node and join them to the cluster.

# on each of your nodes, start the swarm agent
#  <node_ip> doesn't have to be public (eg. 192.168.0.X),
#  as long as the swarm manager can access it.
$ swarm join --advertise=<node_ip:2375> token://<cluster_id>

Finally, we start the Swarm manager. This can be on any machine or even your laptop.

$ swarm manage -H tcp://<swarm_ip:swarm_port> token://<cluster_id>

You can then use regular Docker commands to interact with your swarm.

docker -H tcp://<swarm_ip:swarm_port> info
docker -H tcp://<swarm_ip:swarm_port> run ...
docker -H tcp://<swarm_ip:swarm_port> ps
docker -H tcp://<swarm_ip:swarm_port> logs ...
...

You can also list the nodes in your cluster.

swarm list token://<cluster_id>
<node_ip:2375>

Using a static file describing the cluster

For each of your nodes, add a line to a file. The node IP address doesn't need to be public as long the Swarm manager can access it.

echo <node_ip1:2375> >> /tmp/my_cluster
echo <node_ip2:2375> >> /tmp/my_cluster
echo <node_ip3:2375> >> /tmp/my_cluster

Then start the Swarm manager on any machine.

swarm manage -H tcp://<swarm_ip:swarm_port> file:///tmp/my_cluster

And then use the regular Docker commands.

docker -H tcp://<swarm_ip:swarm_port> info
docker -H tcp://<swarm_ip:swarm_port> run ...
docker -H tcp://<swarm_ip:swarm_port> ps
docker -H tcp://<swarm_ip:swarm_port> logs ...
...

You can list the nodes in your cluster.

$ swarm list file:///tmp/my_cluster
<node_ip1:2375>
<node_ip2:2375>
<node_ip3:2375>

Using etcd

On each of your nodes, start the Swarm agent. The node IP address doesn't have to be public as long as the swarm manager can access it.

swarm join --advertise=<node_ip:2375> etcd://<etcd_ip>/<path>

Start the manager on any machine or your laptop.

swarm manage -H tcp://<swarm_ip:swarm_port> etcd://<etcd_ip>/<path>

And then use the regular Docker commands.

docker -H tcp://<swarm_ip:swarm_port> info
docker -H tcp://<swarm_ip:swarm_port> run ...
docker -H tcp://<swarm_ip:swarm_port> ps
docker -H tcp://<swarm_ip:swarm_port> logs ...
...

You can list the nodes in your cluster.

swarm list etcd://<etcd_ip>/<path>
<node_ip:2375>

Using consul

On each of your nodes, start the Swarm agent. The node IP address doesn't need to be public as long as the Swarm manager can access it.

swarm join --advertise=<node_ip:2375> consul://<consul_addr>/<path>

Start the manager on any machine or your laptop.

swarm manage -H tcp://<swarm_ip:swarm_port> consul://<consul_addr>/<path>

And then use the regular Docker commands.

docker -H tcp://<swarm_ip:swarm_port> info
docker -H tcp://<swarm_ip:swarm_port> run ...
docker -H tcp://<swarm_ip:swarm_port> ps
docker -H tcp://<swarm_ip:swarm_port> logs ...
...

You can list the nodes in your cluster.

swarm list consul://<consul_addr>/<path>
<node_ip:2375>

Using zookeeper

On each of your nodes, start the Swarm agent. The node IP doesn't have to be public as long as the swarm manager can access it.

swarm join --advertise=<node_ip:2375> zk://<zookeeper_addr1>,<zookeeper_addr2>/<path>

Start the manager on any machine or your laptop.

swarm manage -H tcp://<swarm_ip:swarm_port> zk://<zookeeper_addr1>,<zookeeper_addr2>/<path>

You can then use the regular Docker commands.

docker -H tcp://<swarm_ip:swarm_port> info
docker -H tcp://<swarm_ip:swarm_port> run ...
docker -H tcp://<swarm_ip:swarm_port> ps
docker -H tcp://<swarm_ip:swarm_port> logs ...
...

You can list the nodes in the cluster.

swarm list zk://<zookeeper_addr1>,<zookeeper_addr2>/<path>
<node_ip:2375>

Using a static list of IP addresses

Start the manager on any machine or your laptop

swarm manage -H <swarm_ip:swarm_port> nodes://<node_ip1:2375>,<node_ip2:2375>

Or

swarm manage -H <swarm_ip:swarm_port> <node_ip1:2375>,<node_ip2:2375>

Then use the regular Docker commands.

docker -H <swarm_ip:swarm_port> info
docker -H <swarm_ip:swarm_port> run ...
docker -H <swarm_ip:swarm_port> ps
docker -H <swarm_ip:swarm_port> logs ...
...

Range pattern for IP addresses

The file and nodes discoveries support a range pattern to specify IP addresses, i.e., 10.0.0.[10:200] will be a list of nodes starting from 10.0.0.10 to 10.0.0.200.

For example for the file discovery method.

$ echo "10.0.0.[11:100]:2375"   >> /tmp/my_cluster
$ echo "10.0.1.[15:20]:2375"    >> /tmp/my_cluster
$ echo "192.168.1.2:[2:20]375"  >> /tmp/my_cluster

Then start the manager.

swarm manage -H tcp://<swarm_ip:swarm_port> file:///tmp/my_cluster

And for the nodes discovery method.

swarm manage -H <swarm_ip:swarm_port> "nodes://10.0.0.[10:200]:2375,10.0.1.[2:250]:2375"

Contributing a new discovery backend

Contributing a new discovery backend is easy, simply implement this interface:

type Discovery interface {
     Initialize(string, int) error
     Fetch() ([]string, error)
     Watch(WatchCallback)
     Register(string) error
}

Initialize

The parameters are discovery location without the scheme and a heartbeat (in seconds).

Fetch

Returns the list of all the nodes from the discovery.

Watch

Triggers an update (Fetch). This can happen either via a timer (like token) or use backend specific features (like etcd).

Register

Add a new node to the discovery service.

Docker Swarm documentation index

• User guide
• Scheduler strategies
• Scheduler filters
• Swarm API