You can use Portworx to provide storage for your Docker Swarm services. Portworx pools your servers capacity and turns your servers or cloud instances into converged, highly available compute and storage nodes. This section describes how to deploy PX within a Docker Swarm cluster and have PX provide highly available volumes to any application deployed via Docker Swarm.

Below steps demonstrate how to set up a three-node cluster for mysql.

Deploy PX container

Refer to Run with Docker to deploy the Portworx container & create a cluster.

Create a volume

docker volume create -d pxd --name mysql_volume --opt \
        size=4 --opt block_size=64 --opt repl=3 --opt fs=ext4
  • This command creates a volume called mysql_volume.
  • This volume has a replication factor of 3, which means that the data will be protected on 3 separate nodes.

Add labels on Swarm nodes

First, get the replica set for the mysql_volume using the pxctl CLI.

sudo /opt/pwx/bin/pxctl volume inspect mysql_volume

    Volume : 27052673284397061
    Name : mysql_volume
    Size : 4.0 GiB
    Format : ext4
    HA : 3
    IO Priority : LOW
    Creation time : Apr 4 22:23:32 UTC 2017
    Shared : no
    Status : up
    State : detached
    Reads : 0
    Reads MS : 0
    Bytes Read : 0
    Writes : 0
    Writes MS : 0
    Bytes Written : 0
    IOs in progress : 0
    Bytes used : 130 MiB
    Replica sets on nodes:
        Set 0
            Node : 192.168.56.103
            Node : 192.168.56.104
            Node : 192.168.56.105

For each node you see in the replica sets section of the above output, find the corresponding Docker Swarm node. You can use docker node ls and docker node inspect commands for this purpose.

Once you find the nodes, add a label to each of those nodes as below.

docker node update --label-add mysql_volume=true <node_id>

The label mysql_volume=true implies that the node hosts volume mysql_volume’s data.

Create a service

We will now create a mysql service using the newly created volume.

We will use service constraints to influence on which worker node Swarm schedules a container (task) based on the container volume’s data location.

docker service create \
    -p 3306:3306 \
    -e MYSQL_ROOT_PASSWORD=password \
    --name=pxmysql \
    --replicas 3 \
    --mount type=volume,source=mysql_volume,target=/var/lib/mysql \
    --constraint 'node.labels.mysql_volume == true' \
    mysql
  • Note how the volume binding is done via --mount. This causes the Portworx mysql_volume to get bind mounted at /var/lib/mysql, which is where the mysql Docker container stores it’s data.
  • Also note how we put a constraint using --constraint 'node.labels.mysql_volume == true'.

Now Docker Swarm will place the mysql container only on Swarm nodes that contain our volume’s data locally leading to great I/O performance.

You can read more about Swarm service creation here.

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