analytics-platform-go-unidler

README

go-unidler

Unidle idled tools

This is performing the reverse operation of the idler.

This is a rewrite of unidler in Go.

Usage

A Makefile is provided to enable easily building, testing and running the unidler.

make help

Show list of available "commands" (targets)

make run

Compiles and runs the unidler on http://localhost:8080 (or the $PORT specified)

make test

Compiles the test code and runs it

make static (default)

Compiles the unidler to a static-linked binary

make docker-image

Builds a docker image as defined in Dockerfile

make docker-run

Builds and runs the unidler in a docker container

Configuration

The application doesn't require any configuration to work.

Env variable	Default	Details
PORT	:8080	port on which the server listen
UNIDLE_KEY_LABEL	"host"	label used to find kubernetes resources belonging to app to unidle. This is introduced to maintain compatibility with old alpha cluster. Set to "unidle-key" in new prod. TODO: Remove once alpha cluster is retired

NOTE: The server will try to load the kubernetes configuration from in-cluster first (this is the case when running the server within a k8s cluster) and fallback to load it from $HOME/.kube/config when this fails.

If that fails as well the server will not start.

Endpoints

/

This endpoint will render and send the unidling page. This page is mostly responsible to show progress to the user and any error which occurs.

The frontend uses EventSource which will open a persisten connection to the /events endpoint. This is how the user (client) receives the updates on the uniding process from the unidler (server).

/events/ (Server Sent Events)

Requests to /events/ will trigger the unidling process.

Roughly, the unidler will perform the following operations:

• set the Deployment's replicas back to whatever number of replicas there were before the app was unidled (or 1 if that can't be determined)
• wait for the Deployment to have available replicas
• remove metadata information (label/annotation) that are present when an app is idled.
  • this is important at the moment because the idler will assume an app is already idled if it finds this metadata
• Update the app service to point to the app's pods
  • when an app is idled the service will direct traffic to the unidler

Requests to this endpoint will be held open, and Server Side Events with progress updates will be pushed back to the browser as the Deployment corresponding to the Host header is being unidled.

/healthz (healthcheck)

This will responde with a 200 OK and a brief text body. It's used by kubernetes (or wathever) to check that the server is still responding.

Dependencies

Dependencies are managed Using Go Modules.

Dependences are vendored in the /vendor which is checked in Git.

Add a new dependency

To add a dependency:

$ go get foo/bar

Upgrade a dependency

To upgrade a dependency:

$ go get foo/bar

This will upgrade to the latest version of foo/bar with a semver tag. Alternatively, go get foo/bar@v1.2.3 will get a specific version.

Docker image

The Dockerfile uses 2 stages one for building and the final image.

builder stage

final stage

The actual image running go-unidler is just scratch with the binary compiled statically (-ldflags '-extldflags "-static"') to keep the docker image to the minimum.

See this article on containerising Go application: https://www.cloudreach.com/blog/containerize-this-golang-dockerfiles/