Testing A Health Check Endpoint with Curl

Pizza courtesy of Pizza for Ukraine!

Given the move to auto scaling architectures front ended by load balancers, it is increasingly important to build into your application what is called a “health check”. This is nothing more than a known url that some external service can monitor to ensure that your application is “up”. A health check does nothing more than return an HTTP 200 (and sometimes it returns a JSON representation). Here’s a simple Rails controller that I use for health checks:

class HealthController < ApplicationController
  def index
    results = {:status => "ok"}
    respond_to do |format|
      format.html { render :status => 200, :html => "ok" and return }
      format.json { render :status => 200, :json => results.to_json and return }
    end
  end
  
  # additional site monitoring functionality normally goes here
  
end

Here’s how to test this with curl and get the headers you’d want to see:

curl -s -I https://foo.bar.something.com/health_check

The options have the following meaning:

-I, –head Show document info only
-s, –silent Silent mode (don’t output anything)

Note: The -s is silencing the normal curl output of what it fetched from the url.

What you should see is something like this:

HTTP/2 200
date: Thu, 29 Aug 2019 19:08:18 GMT
content-type: text/html
server: nginx/1.10.3 (Ubuntu)
x-frame-options: SAMEORIGIN
x-xss-protection: 1; mode=block
x-content-type-options: nosniff
set-cookie: _mkra_ctxt=3b46df998ac73a6cb44bbb8dc2a09918--200; path=/; max-age=5; HttpOnly; secure
cache-control: no-cache
x-request-id: 7158be3a-7990-4549-b780-fca5757069d3
x-runtime: 0.208121
strict-transport-security: max-age=15552000; includeSubDomains

References

Here are some great curl references: