Heartbeat

Heartbeat is a lightweight daemon that you install on a remote server to periodically check the status of your services and determine whether they are available. Unlike Metricbeat, which only tells you if your servers are up or down, Heartbeat tells you whether your services are reachable.

Heartbeat is useful when you need to verify that you’re meeting your service level agreements for service uptime. It’s also useful for other scenarios, such as security use cases, when you need to verify that no one from the outside can access services on your private enterprise server.

You can configure Heartbeat to ping all DNS-resolvable IP addresses for a specified hostname. That way, you can check all services that are load-balanced to see if they are available.

When you configure Heartbeat, you specify monitors that identify the hostnames that you want to check. Each monitor runs based on the schedule that you specify. For example, you can configure one monitor to run every 10 minutes, and a different monitor to run between the hours of 9:00 and 17:00.

Heartbeat currently supports monitors for checking hosts via:

  • ICMP (v4 and v6) Echo Requests. Use the icmp monitor when you simply want to check whether a service is available. This monitor requires root access.
  • TCP. Use the tcp monitor to connect via TCP. You can optionally configure this monitor to verify the endpoint by sending and/or receiving a custom payload.
  • HTTP. Use the http monitor to connect via HTTP. You can optionally configure this monitor to verify that the service returns the expected response, such as a specific status code, response header, or content.

Goal

When completed, the HA setup will consist of two Ubuntu 14.04 servers in an active/passive configuration. This will be accomplished by pointing a Floating IP, which is how your users will access your services or website, to point to the primary, or active, server unless a failure is detected. In the event that the Heartbeat service detects that the primary server is unavailable, the secondary server will automatically run a script to reassign the Floating IP to itself via the DigitalOcean API. Thus, subsequent network traffic to the Floating IP will be directed to your secondary server, which will act as the active server until the primary server becomes available again (at which point, the primary server will reassign the Floating IP to itself).

To achieve this goal, we will follow these steps:

  • Create 2 Droplets that will receive traffic
  • Create Floating IP and assign it to one of the Droplets
  • Create DNS A record that points to Floating IP (optional)
  • Install Heartbeat on Droplets
  • Configure Heartbeat to Run Floating IP Reassignment Service
  • Create Floating IP Reassignment Service
  • Test failover

Prerequisites

In order to automate the Floating IP reassignment, we must use the DigitalOcean API. This means that you need to generate a Personal Access Token (PAT), which is an API token that can be used to authenticate to your DigitalOcean account, with reading and write access by following the How To Generate a Personal Access Token section of the API tutorial. Your PAT will be used in a script that will be added to both servers in your cluster, so be sure to keep it somewhere safe—as it allows full access to your DigitalOcean account—for reference.

In addition to the API, this tutorial utilizes the following DigitalOcean features:

  • Floating IPs
  • Metadata
  • User Data (Cloud-Config scripts)

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