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3.8 KiB
Markdown
92 lines
No EOL
3.8 KiB
Markdown
# Windows workers for Servo on Taskcluster
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The `servo-win2016` worker type runs short-lived Windows 2016 workers on EC2.
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## AMIs
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Unlike Linux tasks on `docker-worker` where each tasks is executed in a container
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based on a Docker image provided with the task,
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Windows tasks on Taskcluster are typically run by `generic-worker`
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where tasks are executed directly in the worker’s environment.
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So we may want to install some tools globally on the system, to make them available to tasks.
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With the [AWS provisioner], this means building a custom AMI.
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We need to boot an instance on a base Windows AMI,
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install what we need (including `generic-worker` itself),
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then take an image of that instance.
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The [`worker_types`] directory in `generic-worker`’s repository
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has some scripts that automate this,
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in order to make it more reproducible than clicking around.
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The trick is that a PowerShell script to run on boot can be provided
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when starting a Windows instance on EC2, and of course AWS has an API.
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[AWS provisioner]: https://docs.taskcluster.net/docs/reference/integrations/aws-provisioner/references/api
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[`worker_types`]: https://github.com/taskcluster/generic-worker/blob/master/worker_types/
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## Building and deploying a new image
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* Install and configure the [AWS command-line tool].
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* Make your changes to `first-boot.ps1` and/or `base-ami.txt`.
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* Run `python3 build-ami.py`. Note that it can take many minutes to complete.
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* Save the administrator password together with the image ID
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in Servo’s shared 1Password account, in the *Taskcluster Windows AMIs* note.
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* In the [worker type definition], edit `ImageId` and `DeploymentId`.
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Note that the new worker type definition will only apply to newly-provisionned workers.
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`DeploymentId` can be any string. It can for example include the image ID.
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Workers check it between tasks (if `checkForNewDeploymentEverySecs` since the last check).
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If it has changed, they shut down in order to leave room for new workers with the new definition.
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The [EC2 Resources] page has red *Terminate All Instances* button,
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but that will make any running task fail.
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[AWS command-line tool]: https://docs.aws.amazon.com/cli/latest/userguide/cli-chap-welcome.html
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[worker type definition]: https://tools.taskcluster.net/aws-provisioner/servo-win2016/edit
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[EC2 Resources]: https://tools.taskcluster.net/aws-provisioner/servo-win2016/resources
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## FIXME: possible improvement
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* Have a separate staging worker type to try new AMIs without affecting the production CI
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* Automate cleaning up old, unused AMIs and their backing EBS snapshots
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* Use multiple AWS regions
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* Use the Taskcluster API to automate updating worker type definitions?
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## Picking a base AMI
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Amazon provides an ovewhelming number of different Windows images,
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so it’s hard to find what’s relevant.
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Their console might show a paginated view like this:
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> ⇤ ← 1 to 50 of 13,914 AMIs → ⇥
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Let’s grep through this with the API:
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```sh
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aws ec2 describe-images --owners amazon --filters 'Name=platform,Values=windows' \
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--query 'Images[*].[ImageId,Name,Description]' --output table > /tmp/images
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< /tmp/images less -S
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```
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It turns out that these images are all based on Windows Server,
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but their number is explained by the presence of many (all?) combinations of:
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* Multiple OS Version
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* Many available locales
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* *Full* (a.k.a. *with Desktop Experience*), or *Core*
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* *Base* with only the OS, or multiple flavors with tools like SQL Server pre-installed
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If we make some choices and filter the list:
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```sh
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< /tmp/images grep 2016-English-Full-Base | less -S
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```
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… we get a much more manageable handlful of images with names like
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`Windows_Server-2016-English-Full-Base-2018.09.15` or other dates.
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Let’s set `base-ami.txt` to `Windows_Server-2016-English-Full-Base-*`,
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and have `build-ami.py` pick the most recently-created AMI whose name matches that pattern. |