From 31484f5ec52e8193ab7ee9b6616afc0055136287 Mon Sep 17 00:00:00 2001
From: verita84 <verita84@protonmail.com>
Date: Fri, 18 Dec 2020 15:34:02 +0000
Subject: [PATCH]

---
 ...matic-Container-failover-to-other-hosts.md | 61 +++++++++++++++++++
 1 file changed, 61 insertions(+)
 create mode 100644 Automatic-Container-failover-to-other-hosts.md

diff --git a/Automatic-Container-failover-to-other-hosts.md b/Automatic-Container-failover-to-other-hosts.md
new file mode 100644
index 0000000..ef60f7e
--- /dev/null
+++ b/Automatic-Container-failover-to-other-hosts.md
@@ -0,0 +1,61 @@
+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.
\ No newline at end of file