picluster

Table of Contents

Overview of the process
Prerequisites
How to assign container_host_constraints to a container and hosts?
Sample configuration and Testing

This feature will automatically migrate a container to another host after three failed heartbeat attempts. It is recommended to use a Git repository for your Dockerfile's to easily build and move containers across nodes. For applications require data persistence using Docker volumes, it is best to use a distributed filesytem like GlusterFS or NFS so the container will have access to it's data on any host.

Overview of the process

When container_host_constraints is enabled in config.json, each failed heartbeat attempt to a container is logged. When three failed heartbeat attempts occur, the following action is taken:

A new host is chosen randomly from the container map that you designated in container_host_constraints.
The container is deleted on it's current host.
The configuration file is updated with the new host layout.
The container image is built and run on the new host.

Prerequisites

Heartbeat configured in config.json (automatic_heartbeat,heartbeat_interval, and container added to heartbeat section) container_host_constraints enabled in config.json

"container_host_constraints": [],

How to assign container_host_constraints to a container and hosts?

Manually in config.json
Once container_host_constraints is enabled in config.json, you can add the hosts when you choose Add Container in the web console.

Sample configuration and Testing

The following config.json is a minimal configuration needed to try this out on your laptop. It consists of two nodes (localhost and 127.0.0.1) that will run Minio in a container. Currently, Minio is only on the node called localhost.

{
  "token": "1234567890ABCDEFGHJKLMNOP",
  "docker": "../docker",
  "server_port": "3000",
  "agent_port": "3001",
  "layout": [{
      "node": "localhost",
      "minio": "-p 9000:9000"
    },
    {
      "node": "127.0.0.1"
    }
  ],
  "hb": [{
      "node": "localhost",
      "minio": "9000"
    },
    {
      "node": "127.0.0.1"
    }
  ],
  "container_host_constraints": [
    {
      "container": "minio,localhost,127.0.0.1"
    }
  ],
  "automatic_heartbeat": "enabled",
  "heartbeat_interval": "300000",
  "web_username": "admin",
  "web_password": "admin",
  "web_connect": "127.0.0.1",
  "web_port": "3003"
}

Based on the sample above, PiCluster will check if Minio is running every 30 seconds. Since Minio is not created yet, the failover event should start after about 90 seconds.