go-health

A library that enables async dependency health checking for services running on an orchastrated container platform such as kubernetes or mesos.

Why is this important?

Container orchestration platforms require that the underlying service(s) expose a "healthcheck" which is used by the platform to determine whether the container is in a good or bad state.

While this can be achieved by simply exposing a /status endpoint that perfoms synchronous checks against its dependencies (followed by returning a 200 or non-200 status code), it is not optimal for a number of reasons:

• It does not scale
  • The more dependencies you add, the longer your healthcheck will take to complete (and potentially cause your service to be killed off by the orchestration platform).
  • Depending on the complexity of a given dependency, your check may be fairly involved where it is okay for it to take 30s+ to complete.
• It adds unnecessary load on yours deps or at worst, becomes a DoS target
  • Non-malicious scenario
    • Thundering herd problem -- in the event of a deployment (or restart, etc.), all of your service containers are likely to have their /status endpoints checked by the orchestration platform as soon as they come up. Depending on the complexity of the checks, running that many simultaneous checks against your dependencies could cause at worst the dependencies to experience problems and at minimum add unnecessary load.
    • Security scanners -- if your organization runs periodic security scans, they may hit your /status endpoint and trigger unnecessary dep checks.
  • Malicious scenario
    • Loading up any basic HTTP benchmarking tool and pointing it at your /status endpoint could choke your dependencies (and potentially your service).

With that said, not everyone needs asynchronous checks. If your service has one dependency (and that is unlikely to change), it is trivial to write a basic, synchronous check and it will probably suffice.

However, if you anticipate that your service will have several dependencies, with varying degrees of complexity for determing their health state - you should probably think about introducing asynchronous health checks.

How does this library help?

Writing an async healthchecking framework for your service is not a trivial task, especially if Go is not your primary language.

This library:

• Allows you to define how to check your dependencies.
• Allows you to define warning and fatal thresholds.
• Will run your dependency checks on a given interval, in the background. [1]
• Exposes a way for you to gather the check results in a fast and thread-safe manner to help determine the final status of your /status endpoint. [2]
• Comes bundled w/ pre-built checkers for well-known dependencies such as Redis, HTTP.
• Makes it simple to implement and provide your own checkers (by adhering to the checker interface).
• Is test-friendly
  • Provides an easy way to disable dependency health checking.
  • Uses an interface for its dependencies, allowing you to insert fakes/mocks at test time.
• Allows you to trigger listener functions when a health check fails or recovers. [3]

[1] Make sure to run your checks on a "sane" interval - ie. if you are checking your Redis dependency once every five minutes, your service is essentially running blind for about 4.59/5 minutes. Unless you have a really good reason, check your dependencies every X seconds, rather than X minutes.

[2] go-health continuously writes dependency health state data and allows you to query that data via .State(). Alternatively, you can use one of the pre-built HTTP handlers for your /healthcheck endpoint (and thus not have to manually inspect the state data).

[3] By utilizing an implementation of the IStatusListener interface

Example

For full examples, look through the examples dir

1. Create an instance of health and configure a checker (or two)

import (
	health "github.com/InVisionApp/go-health"
	"github.com/InVisionApp/go-health/checkers"
	"github.com/InVisionApp/go-health/handlers"
)

// Create a new health instance
h := health.New()

// Create a checker
myURL, _ := url.Parse("https://google.com")
myCheck, _ := checkers.NewHTTP(&checkers.HTTPConfig{
    URL: myURL,
})

2. Register your check with your health instance

h.AddChecks([]*health.Config{
    {
        Name:     "my-check",
        Checker:  myCheck,
        Interval: time.Duration(2) * time.Second,
        Fatal:    true,
    },
)

3. Start the healthcheck

h.Start()

From here on, you can either configure an endpoint such as /healthcheck to use a built-in handler such as handlers.NewJSONHandlerFunc() or get the current health state of all your deps by traversing the data returned by h.State().

Sample /healthcheck output

Assuming you have configured go-health with two HTTP checkers, your /healthcheck output would look something like this:

{
    "details": {
        "bad-check": {
            "name": "bad-check",
            "status": "failed",
            "error": "Ran into error while performing 'GET' request: Get google.com: unsupported protocol scheme \"\"",
            "check_time": "2017-12-30T16:20:13.732240871-08:00"
        },
        "good-check": {
            "name": "good-check",
            "status": "ok",
            "check_time": "2017-12-30T16:20:13.80109931-08:00"
        }
    },
    "status": "ok"
}

Additional Documentation

• Examples
  • Status Listeners
• Checkers

Contributing

All PR's are welcome, as long as they are well tested. Follow the typical fork->branch->pr flow.