Serf Case

This case shows Hashicorp's Serf product.

• Intro
• Serf Benefits
• Problem Solving
• Running the Agent
  • Starting Agent
  • Checking Cluster members
  • Stopping Agent
• Joining the Cluster
• Leaving the Cluster
• Events
• Custom Events
• Custom Queries

Intro

Serf is a tool for:

• Cluster Membership
• Failure Detection
• De-centralized Orchestration

Serf Benefits

• Decentralized
• Fault Tolerant
• Self-Healing
• Highly Available

Problem Solving

1. Membership
2. Failure Detection & Recovery
3. Custom Event Propagation

Running the Agent

Starting Agent

serf agent

Checking Cluster members

serf members

Stopping Agent

Gracefully Leave

serf leave

or

Ctrl-C

Forcefully Leave

serf force-leave

Joining the Cluster

Starting multiple agents...

serf agent -node=agent-one -bind=127.20.20.10
serf agent -node=agent-one -bind=127.20.20.11

Telling 1st agent to join the 2nd agent will involve going into the 1st agent and telling it to join the 2nd agent:

serf join 127.20.20.11

You can check the status of agents after joining by Checking Cluster members

Leaving the Cluster

To leave just stop the agent you want to leave. See options in Stopping Agent section.

Events

Serf currently invokes the following types of events:

1. member-join
2. member-leave
3. member-failed
4. member-update
5. member-reap
6. user
7. query

Event Handlers

Starting a Serf agent with the event handler.

serf agent -log-level=debug -event-handler=handler.sh

flagging the serf agent in log level debug mode so we can see the stdin/stderr of the events.

Custom Events

To send a custom event we simply do:

serf event [your custom event]

Custom Queries

E.g. to query the load

serf query load

which can then be combined with Custom Events' an Event Handler to send back responses. In this particular example, we can send back load times of machines.