The static/GitLab shim allows [GitLab CI][] to push updates on websites
hosted in the [static mirror system][].

[[_TOC_]]

# Tutorial

## Converting a job from Jenkins

This is how to convert a given website from Jenkins to GitLab CI:

* [ ] include ci-templates `lektor.yml` job
* [ ] site builds and works in gitlab pages
* [ ] [add the deploy-static job and SSH key to GitLab CI](https://gitlab.torproject.org/tpo/tpa/team/-/wikis/service/static-shim#deploying-a-static-site-from-gitlab-ci)
* [ ] [deploy the SSH key and static site in Puppet](https://gitlab.torproject.org/tpo/tpa/team/-/wikis/service/static-shim#adding-a-new-static-site-shim-in-puppet)
* [ ] run the deploy-static job, make sure the site still works and
      was deployed properly (`curl -sI https://example.torproject.org/ | grep -i Last-Modified`)
* [ ] [archive the repo on gitolite](https://gitlab.torproject.org/tpo/tpa/team/-/wikis/howto/gitlab/#how-to-migrate-a-git-repository-from-legacy-to-gitlab)
* [ ] remove the old site on staticiforme
* [ ] [fully retire the Jenkins jobs](https://gitlab.torproject.org/tpo/tpa/team/-/wikis/service/jenkins#removing-a-job)
* [ ] notify users about the migration

Upstream GitLab also has [generic documentation on how to migrate from
Jenkins](https://docs.gitlab.com/ee/ci/migration/jenkins.html) which could be useful for us.

## Deploying a static site from GitLab CI

First, make sure the site builds in [GitLab CI][]. A `build` stage
MUST be used. It should produce the artifacts used by the `deploy`
job, provided in the [`static-shim-deploy.yml` template][]. How to
build the website will vary according to the site, obviously. See the
[Hugo build instructions below](#building-a-hugo-site) for that
specific generator.

[`static-shim-deploy.yml` template]: https://gitlab.torproject.org/tpo/tpa/ci-templates/-/blob/main/static-shim-deploy.yml

TODO: link to documentation on how to build Lektor sites in GitLab CI.

It is a good idea to also add a `pages` stage to preview the
build. The above template has an example `pages` stage, see also the
[publishing GitLab pages](https://gitlab.torproject.org/tpo/tpa/team/-/wikis/howto/gitlab/#publishing-gitlab-pages) section our [GitLab documentation](https://gitlab.torproject.org/tpo/tpa/team/-/wikis/howto/gitlab/).

Then include the deploy job template in the `.gitlab-ci.yml` with a
snippet like this:

```
variables:
  SITE_URL: example.torproject.org
  SUBDIR: public/

include:
  project: tpo/tpa/ci-templates
  file: static-shim-deploy.yml
```

The `SITE_URL` and `SUBDIR` parameters need to be changed to reflect,
respectively, the FQDN of the website as defined in the
`static-components.yml` file, and the directory where the website was
built by the previous build stage. You may also need
`GIT_SUBMODULE_STRATEGY: recursive` if you have submodules (e.g. hugo
themes are often shipped as submodules). For example, for
<https://status.torproject.org>, the `.gitlab-ci.yml` file looks like
this (`build` stage elided for simplicity):

    variables:
      GIT_SUBMODULE_STRATEGY: recursive
      SITE_URL: status.torproject.org
      SUBDIR: public/

    include:
      project: tpo/tpa/ci-templates
      file: static-shim-deploy.yml

Then you also need to set an SSH key in the project. First, generate a
password-less key locally:

    ssh-keygen -f id_rsa -P "" -C "static-shim deploy key"

Then in the project's Settings -> CI/CD -> Variables, pick `Add
variable`, with the following parameters:

 * Key: `STATIC_GITLAB_SHIM_SSH_PRIVATE_KEY`
 * Value: the content of the `id_rsa` file, above (yes, it's the
   private key)
 * Type: `file`
 * Protect variable: checked
 * Masked variable: unchecked

Then the *public* part of that key needs to be added in Puppet. This
can only be done by TPA, so file a ticket there if you need
assistance. For TPA, [see below](#adding-a-new-static-site-shim-in-puppet) for the remaining instructions.

Once you have sent the public key to TPA, you MUST destroy your local
copy of the key, to avoid any possible future leaks.

You can commit the above changes to the `.gitlab-ci.yml` file, but
when pushed, the pipeline's `deploy` stage is normal, TPA needs to do
its magic for the deploy to work. Make sure the build works in GitLab
pages before requesting the deploy in the static mirror system.

# How-to

## Adding a new static site shim in Puppet

The public key mentioned above should be added in the `tor-puppet.git` repository, in the
`hiera/common.yaml` file, in the `staticsync::gitlab_shim::ssh::sites`
hash.

There, the site URL is the key and the public key (only the key part,
no `ssh-rsa` prefix or comment suffix) is the value. For example, this
is the entry for `status.torproject.org`:

    staticsync::gitlab_shim::ssh::sites:
      status.torproject.org: "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"

At this point, the deploy job should be able to `rsync` the content to
the static shim, but the deploy will still fail because the
static-component configuration does not match and the
`static-update-component` step will fail.

To fix this, the static-component entry should be added (or modified,
if it already exists) to point to the shim. This, for example, is how
research is configured right now:

    research.torproject.org:
      master: static-master-fsn.torproject.org
      source: static-gitlab-shim.torproject.org:/srv/static-gitlab-shim/research.torproject.org/public

It was migrated from Jenkins with a commit like this:

    modified   modules/roles/misc/static-components.yaml
    @@ -99,7 +99,7 @@ components:
         source: staticiforme.torproject.org:/srv/research.torproject.org/htdocs-staging
       research.torproject.org:
         master: static-master-fsn.torproject.org
    -    source: staticiforme.torproject.org:/srv/research.torproject.org/htdocs
    +    source: static-gitlab-shim.torproject.org:/srv/static-gitlab-shim/research.torproject.org/public
       rpm.torproject.org:
         master: static-master-fsn.torproject.org
         source: staticiforme.torproject.org:/srv/rpm.torproject.org/htdocs

After commit and push, Puppet needs to run on the shim and master, in
the above case:

    for host in static-gitlab-shim static-master-fsn ; do
        ssh $host.torproject.org puppet agent --test
    done

The next pipeline should now succeed in deploying the site in GitLab.

If the site is migrated from Jenkins, make sure to [remove the old
Jenkins job](service/jenkins#removing-a-job) and make sure the old site is cleared out from the
previous static source:

    ssh staticiforme.torproject.org rm -rf /srv/research.torproject.org/

Typically, you will also want to [archive the git repository](howto/git#archiving-a-repository) if
it hasn't already been [migrated to GitLab](howto/gitlab#how-to-migrate-a-git-repository-from-legacy-to-gitlab).

## Building a Hugo site

Normally, you should be able to deploy a Hugo site by including the
template and setting a few variables. This `.gitlab-ci.yml` file,
taken from the [status.tpo .gitlab-ci.yml](https://gitlab.torproject.org/tpo/tpa/status-site/-/blob/main/.gitlab-ci.yml), should be sufficient:

```
image: registry.gitlab.com/pages/hugo/hugo_extended:0.65.3

variables:
  GIT_SUBMODULE_STRATEGY: recursive
  SITE_URL: status.torproject.org
  SUBDIR: public/

include:
  project: tpo/tpa/ci-templates
  file: static-shim-deploy.yml

build:
  stage: build
  script:
    - hugo
  artifacts:
    paths:
      - public

# we'd like to *not* rebuild hugo here, but pages fails with:
#
# jobs pages config should implement a script: or a trigger: keyword
pages:
  stage: deploy
  script:
    - hugo
  artifacts:
    paths:
      - public
  only:
    - merge_requests
```

See below if this is an old hugo site, however.

### Building an old Hugo site

Unfortunately, because `research.torproject.org` was built a long time
ago, newer Hugo releases broke its theme and the newer versions
(tested 0.65, 0.80, and 0.88) all fail in one way or another. In this
case, you need to jump through some hoops to have the build work
correctly. I did this for `research.tpo`, but you might need a
different build system or Docker images:

```
# use an older version of hugo, newer versions fail to build on first
# run
#
# gohugo.io does not maintain docker images and the one they do
# recommend fail in GitLab CI. we do not use the GitLab registry
# either because we couldn't figure out the right syntax to get the
# old version from Debian stretch (0.54)
image: registry.hub.docker.com/library/debian:buster

include:
  project: tpo/tpa/ci-templates
  file: static-shim-deploy.yml

variables:
  GIT_SUBMODULE_STRATEGY: recursive
  SITE_URL: research.torproject.org
  SUBDIR: public/

build:
  before_script:
    - apt update
    - apt upgrade -yy
    - apt install -yy hugo
  stage: build
  script:
    - hugo
  artifacts:
    paths:
      - public

# we'd like to *not* rebuild hugo here, but pages fails with:
#
# jobs pages config should implement a script: or a trigger: keyword
#
# and even if we *do* put a dummy script (say "true"), this fails
# because it runs in parallel with the build stage, and therefore
# doesn't inherit artifacts the way a deploy stage normally would.
pages:
  stage: deploy
  before_script:
    - apt update
    - apt upgrade -yy
    - apt install -yy hugo
  script:
    - hugo
  artifacts:
    paths:
      - public
  only:
    - merge_requests
```

## Deploy artifacts manually

If a site is not deploying normally, it's still possible to deploy a
site by hand by downloading and extracting the artifacts using the
`static-gitlab-shim-pull` script.

For example, given the [Pipeline 13285](https://gitlab.torproject.org/tpo/tpa/status-site/-/pipelines/13285) has [job 38077](https://gitlab.torproject.org/tpo/tpa/status-site/-/jobs/38077), we can
tell the puller to deploy in debugging mode with this command:

    sudo -u static-gitlab-shim /usr/local/bin/static-gitlab-shim-pull --artifacts-url https://gitlab.torproject.org/tpo/tpa/status-site/-/jobs/38077/artifacts/download --site-url status.torproject.org --debug

The `--artifacts-url` is the `Download` link in the job page. This
will:
 
 1. download the artifacts (which is a ZIP file)
 2. extract them in a temporary directory
 3. `rsync --checksum` them to the actual source directory (to avoid
    spurious timestamp changes)
 4. call `static-update-component` to deploy the site

Note that this script was part of the webhook implementation and might
eventually be retired if that implementation is completely
removed. This logic now lives in the [`static-shim-deploy.yml`
template][].

## Pager playbook

A typical failure will be that users complains that their
`deploy_static` job fails. We have yet to see such a failure occur,
but if it does, users should provide a link to the Job log, which
should provide more information.

## Disaster recovery

### Server lost

The service is "cattle" in that it can easily be rebuilt from scratch
if the server is completely lost. Naturally it strongly depends on
GitLab for operation. If GitLab would fail, it should still be
possible to deploy sites to the static mirror system by deploying them
by hand to the static shim and calling `static-update-component`
there. It would be preferable to build the site outside of the
static-shim server to avoid adding any extra packages we do not need
there.

The status site is particularly vulnerable to disasters here, see the
[status-site disaster recovery documentation](service/status#disaster-recovery) for pointers on where
to go in case things really go south.

### GitLab server compromise

Another possible disaster that could happen is a complete GitLab
compromise or hostile GitLab admin. Such an attacker could deploy any
site they wanted and therefore deface or sabotage critical websites,
introducing hostile code in thousands of users. If such an event would
occur:

 1. **remove all SSH keys from the Puppet configuration**,
    specifically in the `staticsync::gitlab_shim::ssh::sites`
    variable, defined in `hiera/common.yaml`.

 2. restore sites from a known backup. the [backup service](howto/backup) should
    have a copy of the static-shim content

 3. redeploy the sites manually (`static-update-component $URL`)

The static shim server itself should be fairly immune to compromise as
only TPA is allowed to login over SSH, apart from the private keys
configured in the GitLab projects. And those are very restricted in
what they can do (i.e. only `rrsync` and `static-update-component`).

# Reference

## Installation

A new server can be built by installing a regular VM with the
`staticsync::gitlab_shim` class. The server also must have this line
in its LDAP host entry:

    allowedGroups: mirroradm

## SLA

There is no defined SLA for this service right now. Websites should
keep working even if it goes down as it is only a static source, but,
during downtimes, updates to websites are not possible.

## Design

The static shim was built to allow [GitLab CI][] to deploy content to the
[static mirror system][]. 

[GitLab CI]: service/ci

They way it works is that GitLab CI jobs (defined in the
`.gitlab-ci.yml` file) build the site and then push it to a static
source (currently `static-gitlab-shim.torproject.org`) with rsync over
SSH. Then the CI job also calls the `static-update-component` script
for the master to pull the content just like any other static
component.

![SSH deploy design of the static-shim](static-shim/architecture-static-shim-ssh.png)

The sites are deployed on a separate static-source to avoid adding
complexity to the already complicated, general purpose static source
(`staticiforme`). This has the added benefit that the source can be
hardened in the sense that access is restricted to TPA (which is not
the case of `staticiforme`).

The mapping between webhooks and static components is established in
Puppet, which writes the SSH configuration, hard-coding the target
directory which corresponds to the source directory in the
`static-components.yaml` file. This is done to ensure that a given
GitLab project only has access to a single site and cannot overwrite
other sites.

This involves that each site configured in this way must have a secret
token (in GitLab) and configuration (in Hiera) created by TPA in
Puppet. The secret token must also be configured in the GitLab
project. This could be automated by the judicious use of the GitLab
API using admin credentials, but considering that new sites are not
created very frequently, it is currently be done by hand. 

The SSH key is generated by the user, but that could also be managed
by Trocla, although only the newer versions support that
functionality, and that version is not currently available in Debian.

A [previous design](#webhook-deployment) involved a webhook written in Python, but now most
of the business logic resides in a [`static-shim-deploy.yml` template]
template which is basically a shell script embedded in a YAML
file. (We have considered taking this out of the template and writing
a proper Python script, but then users would have to copy that script
over their repo, or clone a repo in CI, and that seems impractical.)

Another thing we considered is to set [instance-level templates](https://docs.gitlab.com/ee/user/admin_area/settings/instance_template_repository.html)
but it seems that feature is not available in GitLab's free software
version.

The CI hooks are deployed by users, which will typically include the
above template in their own `.gitlab-ci.yml` file.

[static mirror system]: howto/static-component

### Storage

Files are generated in GitLab CI as artifacts and stored there, which
makes it possible for them to be [deployed by hand as well](#deploy-artifacts-manually). A copy
is also kept on the static-shim server to make future deployments
faster. We use `rsync --checksum` to avoid updating the timestamps
even if the source file were just regenerated from scratch.

### Authentication

The shim assumes that GitLab projects host a private SSH key and can
access the shim server over SSH with it. Access is granted, by Puppet
(`tor-puppet.git` repository, `hiera/common.yaml` file, in the
`staticsync::gitlab_shim::ssh::sites` hash) only to a specific
site.

The restriction is defined in the `authorized_keys` file, with
`restrict` and `command=` options. The latter restricts the public key
to only a *specific* site update, with a wrapper that will call
`static-update-component` on the right component or `rrsync` which is
`rsync` but limited to a specific directory. We also allow connections
only from GitLab over SSH.

This implies that the `SITE_URL` provided by the GitLab CI job over
SSH, whether it is for the `rsync` or `static-update-component`
commands, is actually ignored by the backend. It is used in the job
definition solely to avoid doing two deploys in parallel to the same
site, through the GitLab [`resource_group`](https://docs.gitlab.com/ee/ci/resource_groups/) mechanism.

The public part of that key should be set in the GitLab project, as a
File variable called `STATIC_GITLAB_SHIM_SSH_PRIVATE_KEY`. This way
the GitLab runners get access to the private key and can deploy those
changes.

The impact of this is that a compromise on GitLab or GitLab CI can
compromise all web sites managed by GitLab CI. While we do restrict
what individual keys can do, a total compromise of GitLab could, in
theory, leak all those private keys and therefore defeat those
mechanisms. See the [disaster recovery section](#disaster-recovery) for how such a
compromise could be recovered from.

The GitLab runners, in turn, authenticate the SSH server through a
[instance-level CI/CD variable](https://docs.gitlab.com/ee/ci/variables/#add-a-cicd-variable-to-an-instance) called
`STATIC_GITLAB_SHIM_SSH_HOST_KEYS` which declares the public SSH host
keys for the server. Those need to be updated if the server is
re-deployed, which is unfortunate. An alternative might be to sign
public keys with an SSH CA (e.g. [this guide](https://blog.liw.fi/posts/2021/09/28/sshca/)) but then the CA
would also need to be present, so it's unclear that would be a
benefit.

## Issues

There is no issue tracker specifically for this project, [File][] or
[search][] for issues in the [team issue tracker][search].

 [File]: https://gitlab.torproject.org/tpo/tpa/team/-/issues/new
 [search]: https://gitlab.torproject.org/tpo/tpa/team/-/issues

This service was designed in [ticket 40364](https://gitlab.torproject.org/tpo/tpa/team/-/issues/40364).

## Maintainer, users, and upstream

The shim was written by anarcat and is maintained by TPA. It is used
by all "critical" websites managed in GitLab.

## Monitoring and testing

There is no specific monitoring for this service, other than the
usual server-level monitoring. If the service should fail, users will
notice because their pipelines start failing.

Good sites to test that the deployment works are
<https://research.torproject.org/> ([pipeline link](https://gitlab.torproject.org/tpo/web/research/-/pipelines), not critical)
or <https://status.torproject.org/> ([pipeline link](https://gitlab.torproject.org/tpo/tpa/status-site/-/pipelines),
semi-critical).

## Logs and metrics

Jobs in GitLab CI have their own logs and retention policies. The
static shim should not add anything special to this, in theory. In
practice it's possible some private key leakage occurs if a user would
display the content of their own private SSH key in the job log. If
they use the provided template, this should not occur.

We do not maintain any metrics on this service, other than the
usual server-level metrics.

## Backups

No specific backup procedure is necessary for this server, outside of
the automated basics. In fact, data on this host is mostly ephemeral
and could be reconstructed from pipelines in case of a total server
loss.

As mentioned in the [disaster recovery section](#disaster-recovery), if the GitLab
server gets compromised, the backup should still contain previous
good copies of the websites, in any case.

## Other documentation

 * [TPA-RFC-10][]: Jenkins retirement
 * GitLab's [CI deployment mechanism](https://about.gitlab.com/blog/2021/02/05/ci-deployment-and-environments/) blog post
 * [Design and launch ticket](https://gitlab.torproject.org/tpo/tpa/team/-/issues/40364)
 * our [static mirror system][] documentation
 * our [GitLab CI documentation][GitLab CI]
 * [Webhook homepage](https://github.com/adnanh/webhook)
   * [hook definition documentation](https://github.com/adnanh/webhook/blob/master/docs/Hook-Definition.md)
   * [hook examples](https://github.com/adnanh/webhook/blob/master/docs/Hook-Examples.md)
   * [hook rules](https://github.com/adnanh/webhook/blob/master/docs/Hook-Rules.md)
   * [how to refer to payload in hook configuration](https://github.com/adnanh/webhook/blob/master/docs/Referencing-Request-Values.md)
   * [usage](https://github.com/adnanh/webhook/blob/master/docs/Webhook-Parameters.md)
 * [GitLab webhook documentation](https://docs.gitlab.com/ee/user/project/integrations/webhooks.html)

# Discussion

## Overview

The static shim was built to unblock the [Jenkins retirement
project](https://gitlab.torproject.org/groups/tpo/-/milestones/27) ([TPA-RFC-10][]). A key blocker was that the [static mirror system][] was
strongly coupled with Jenkins: many high traffic and [critical websites](policy/tpa-rfc-10-jenkins-retirement#critical-website-builds)
are built and deployed by Jenkins. Unless we wanted to completely
retire the static mirror system (in favor, say, of GitLab Pages), we
had to create a way for GitLab CI to deploy content to the static
mirror system.

[TPA-RFC-10]: policy/tpa-rfc-10-jenkins-retirement

This section contains more in-depth discussions about the reasoning
behind the project, discarded alternatives, and other ideas.

## Goals

Note that those goals were actually written down once the server was
launched, but they were established mentally before and during the
deployment.

### Must have

 * deploy sites from GitLab CI to the static mirror system
 * site A cannot deploy to site B without being explicitly granted
   permissions
 * server-side (i.e. in Puppet) access control (i.e. user X can only
   deploy site B)

### Nice to have

 * automate migration from Jenkins to avoid manually doing many sites
 * reusable GitLab CI templates

### Non-Goals

 * static mirror system replacement

## Approvals required

TPA, part of [TPA-RFC-10][]: Jenkins retirement.

## Proposed Solution

We have decided to deploy sites over SSH from GitLab CI, see below for
a discussion.

## Cost

One VM, 20-30 hours of work, see [tpo/tpa/team#40364](https://gitlab.torproject.org/tpo/tpa/team/-/issues/40364) for time tracking.

## Alternatives considered

This shim was designed to replace Jenkins with GitLab CI.  The various
options considered are discussed here, see also the [Jenkins
documentation](service/jenkins#gitlab-ci) and [ticket 40364](https://gitlab.torproject.org/tpo/tpa/team/-/issues/40364).

### CI deployment

We considered using GitLab's [CI deployment mechanism](https://about.gitlab.com/blog/2021/02/05/ci-deployment-and-environments/) instead of
webhooks, but originally decided against it for the following reasons:

 * the complexity is similar: both need a shared token (webhook secret
   vs SSH private key) between GitLab and the static source (the
   webhook design, however, does look way more complex than the deploy
   design, when you compare the two diagrams)

 * however, configuring the deployment variables takes more click
   ([9](https://gitlab.torproject.org/tpo/tpa/status-site/-/settings/ci_cd) vs [5](https://gitlab.torproject.org/tpo/tpa/status-site/-/hooks) in my count), and is slightly more confusing
   (e.g. what's "Protect variable"?) and possibly insecure
   (e.g. private key leakage if user forgets to click "Mask variable")

 * the deployment also requires custom code to be added to the
   `.gitlab-ci.yml` file. in the context where we are considering
   using GitLab pages to replace the static mirror system in the long
   term, we prefer to avoid adding custom stuff to the CI
   configuration file and "pretend" that this is "just like GitLab
   pages"

 * we prefer to open a HTTPS port than an SSH port to GitLab, from a
   security perspective, even if the SSH user would be protected by an
   proper `authorized_keys`. in the context where we could consider
   locking down SSH access to only jump boxes, it would require an
   exception and is more error prone (e.g. if we somehow forget the
   `command=` override, we open full shell access)

After trying the webhook deployment mechanism (below), we decided to
go back to the deployment mechanism instead. See below for details on
the reasoning, and above for the full design of the current
deployment.

### webhook deployment

A designed based on GitLab webhooks was established, with a workflow
that goes something like this:

 1. user pushes a change to GitLab, which ...
 2. triggers a CI pipeline
 3. CI runner picks up the jobs and builds the website, pushes the
    artifacts back to GitLab
 4. GitLab fires a [webhook](https://gitlab.torproject.org/help/user/project/integrations/webhooks#pipeline-events), typically on [pipeline events](https://docs.gitlab.com/ee/user/project/integrations/webhooks.html#pipeline-events)
 5. webhook receives the ping and authenticates against a
    configuration, mapping to a given `static-component`
 6. after authentication, the webhook fires a script
    (`static-gitlab-shim-pull`)
 7. `static-gitlab-shim-pull` parses the payload from the webhook and
    finds the URL for the artifacts
 8. it extracts the artifacts in a temporary directory
 9. it runs `rsync -c` into the local static source, to avoid
    resetting timestamps
 10. it fires the static-update-component command to propagate changes
     to the rest of the static-component system

A subset of those steps can be seen in the following design:

![Design of the static-shim](static-shim/architecture-static-shim.png)

The shim components runs on a separate static-source, called
`static-gitlab-shim-source`. This is done to avoid adding complexity
to the already complicated, general purpose static source
(`staticiforme`). This has the added benefit that the source can be
hardened in the sense that access is restricted to TPA (which is not
the case of `staticiforme`).

The mapping between webhooks and static components is established in
Puppet, which generates the secrets and writes it to the webhook
configuration, along with the `site_url` which corresponds to the site
URL in the `static-components.yaml` file. This is done to ensure that
a given GitLab project only has access to a single site and cannot
overwrite other sites.

This involves that each site configured in this way must have a
secret token (in Trocla) and configuration (in Hiera) created by TPA
in Puppet. The secret token must also be configured in the GitLab
project. This could be automated by the judicious use of the GitLab
API using admin credentials, but considering that new sites are not
created very frequently, it could also be done by hand.

Unfortunately this design has two major flaws:

 1. webhooks are [designed to be fast and short-lived](https://docs.gitlab.com/ee/user/project/integrations/webhooks.html#webhook-endpoint-tips): most site
    deployments take longer than the pre-configured webhook timeout (10
    seconds) and therefore cannot be deployed synchronously, which
    implies that...

 2. webhook cannot propagate deployment errors back to the user
    meaningfully: even if they run synchronously, errors in webhooks
    do not show up in the CI pipeline, assuming the webhook manages to
    complete at all. if the webhook fails to complete in time, no
    output is available to the user at all. running asynchronously is
    even worse as deployment errors do not show up in GitLab at all
    and would require special monitoring by TPA, instead of delegating
    that management to users. It is possible to to see the list of
    recent webhook calls, in Settings -> Webhooks -> Edit ->
    Recent deliveries. But that is rather well-hidden.

Note that it may have been possible to change the 10 seconds timeout
with:

    gitlab_rails['webhook_timeout'] = 10

in the `/etc/gitlab/gitlab.rb` file ([source](https://docs.gitlab.com/ee/user/project/integrations/webhooks.html#webhook-fails-or-multiple-webhook-requests-are-triggered)). But static site
deployments can take a while, so it's not clear at all we can actually
wait for the full deployment.

In the short term, the webhook system has be used asynchronously (by
removing the `include-command-output-in-response` parameter in the
webhook config), but then the error reporting is even worse because
the caller doesn't even know if the deploy succeeds or fails.

We have since moved to the deployment system documented in the [design
section](#design).

### GitLab "Integrations"

Another approach we briefly considered is to write an [integration](https://docs.gitlab.com/ee/user/project/integrations/overview.html)
into GitLab. We found the documentation for this was nearly
nonexistent. It also meant maintaining a bundle of Ruby code inside
GitLab, which seemed impractical, at best.
