Help:Toolforge/Kubernetes

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Toolforge

Kubernetes (often abbreviated k8s) is a platform for running containers. It is used in Toolforge to isolate Tools from each other and allow distributing Tools across a pool of servers.

Kubernetes webservices

The Toolforge webservice command has a --backend=kubernetes mode that will start, stop, and restart containers designed to run web services for various languages. See our Webservice help for more details.

Kubernetes cronjobs

It is possible to run cron jobs on kubernetes (see upstream documentation for a full description), however this functionality is not officially supported by the Wikimedia Cloud Services team and should be considered an experimental feature.

Kubernetes continuous jobs

The basic unit of managing execution on a Kubernetes cluster is called a "deployment". Each deployment is described with a YAML configuration file which describes the container images to be started ("pods" in the Kubernetes terminology) and commands to be run inside them after the container is initialized. A deployment also specifies where the pods run and what external resources are connected to them. The upstream documentation is comprehensive.

Example deployment.yaml

Stashbot is a Python irc bot that runs in a Kubernetes deployment. The deployment.yaml file that it uses to tell Kubernetes how to start the bot is reproduced below. This deployment is launched using a stashbot.sh wrapper script which runs kubectl create -f /data/project/stashbot/etc/deployment.yaml.

This deployment:

  • Uses the 'stashbot' namespace that the tool is authorized to control
  • Creates a container using the 'latest' version of the 'docker-registry.tools.wmflabs.org/toollabs-python2-base' Docker image.
  • Runs the command /data/project/stashbot/bin/stashbot.sh run when the container starts.
  • Mounts the /data/project/stashbot/ NFS directory as /data/project/stashbot/ inside the container.

Monitoring your jobs

You can see which jobs you have running with kubectl get pods. Using the name of the pod, you can see the logs with kubectl logs <pod-name>.

To restart a failing pod, use kubectl delete <pod-name>. If you need to kill it entirely, find the deployment name with kubectl get deployment, and delete it with kubectl delete deployment <deployment-name>.

Namespaces

Each tool has been granted control of a Kubernetes "namespace". Your tool can only create and control objects in its namespace. A tool's namespace is the same as the tool's name (e.g. admin, stashbot, hay, etc).

Container images

The Toolforge Kubernetes cluster is restricted to loading Docker images published at docker-registry.tools.wmflabs.org (see Portal:Toolforge/Admin/Kubernetes#Docker_Images for more information). These images are built using the Dockerfiles in the operations/docker-images/toollabs-images git repository.

Available container types

The webservice command has an optional type argument that allows you to choose which Docker container to run your Tool in.

Currently provided types:

  • golang
  • jdk8
  • nodejs
  • php5.6
  • php7.2
  • python
  • python2
  • ruby2
  • tcl

For example to start a webservice using a php7.2 container, run:

webservice --backend=kubernetes php7.2 start

A list of images is available in the overview page of the images source code repository for the Toolforge (each folder name represents a Docker image) and via the Docker registry catalog.

As of Feb 2018, we don't support mixed runtime containers. This may change in the future. Also, we don't support "bring your own container" on our kubernetes (yet!). And there is no mechanism for an user to install system packages inside of a container.

PHP

PHP uses lighttpd as a webserver, and looks for files in ~/public_html/.

Versions & Packages

There are two versions of PHP available, PHP 7.2 (on Debian Stretch), and the legacy PHP 5.6 (on Debian Jessie). This is mostly compatible with PHP 5.5 which is present on the legacy GridEngine Ubuntu Trusty nodes - so if your web service is currently running on Trusty with GridEngine, it should work on Kubernetes.

You can view the installed PHP extensions on the phpinfo tool. This should match the PHP related packages installed on GridEngine exec nodes. Additional packages can be added on request by creating a subtask of T140110.

nodejs

The container images for Node.js, such as docker-registry.tools.wmflabs.org/toollabs-nodejs-base:latest currently come with a current version of Node.js LTS from Wikimedia APT (as of September 2018, this is Node.js 6). This is the same version used by Wikimedia Foundation in production and for continuous integration.

Broken npm

Given npm is not suitable for use in Wikimedia production, the version of Node.js provided by Wikimedia APT is compiled without npm. (Unlike the official Node.js distribution.) And because there is no use for npm in Wikimedia production, there is no "npm" Debian package maintained in Wikimedia APT. The result is that the only "npm" Debian package available is the one from upstream Debian, which is npm 1.4 which was originally bundled in 2014 with Node 0.10 (debian/npm, debian/nodejs). This version is EOL and is incompatible with most packages on the npmjs.org registry. To update it within your container, follow these steps

# Step 1: Start a shell in your Node.js pod (see "Shell" section below)
tool@tools-login$ kubectl exec -it podname-123-aaa -- /bin/bash

# Step 2: Create $HOME/bin and ensure it is in your PATH
podname:/data/project/tool$ mkdir bin/
podname:/data/project/tool$ export PATH="${HOME}/bin:${PATH}"
# To avoid having to re-export PATH every time you use your tool, add the export command to your .bashrc file!

# Step 3: Use npm to install 'npm'
podname:/data/project/tool$ npm install npm
....
# This installs the current version of npm at node_modules/.bin/npm

# Step 4: Create a symlink in $HOME/bin
podname:/data/project/tool$ ln -s $HOME/node_modules/.bin/npm $HOME/bin/npm
# Close the shell and create a new shell (to initialise PATH)
podname:/data/project/tool$ exit
tool@tools-login$ kubectl exec -it podname-123-aaa -- /bin/bash
podname:/data/project/tool$

# Step 5: Verify that you now use a current npm instead of npm 1.4
podname:/data/project/tool$ npm --version
6.4.1 

Shell

To establish a shell inside your Kubernetes pod, run the following two commands from tools-login:

$ kubectl get pods
NAME                          READY     STATUS    RESTARTS   AGE
perflogbot-2167463494-5uqkh   1/1       Running   4          6d

Choose the name of the pod you want to start an interactive shell with, and run kubectl exec -it <podname> -- /bin/bash . For example:

$ kubectl exec -it perflogbot-2167463494-5uqkh -- /bin/bash

<flogbot-2167463494-5uqkh:/data/project/perflogbot$

See also Get a Shell to a Running Container at kubernetes.io/docs.

See also