zulip/docs/testing/continuous-integration.md

# Continuous integration (CI)

The Zulip server uses [CircleCI](https://circleci.com/) and
[Travis CI](https://travis-ci.org/) for continuous
integration. CircleCI is the primary CI, and runs frontend and backend
tests across a wide range of Ubuntu distributions. Travis CI is
legacy, used only for running the end-to-end production installer
test.  This page documents useful tools and tips to know about when
using CircleCI and Travis CI and debugging issues with them.

## Goals

The overall goal of our CI is to avoid regressions and minimize the
total time spent debugging Zulip.  We do that by trying to catch as
many possible future bugs as possible, while minimizing both latency
and false positives, both of which can waste a lot of developer time.
There are a few implications of this overall goal:

* If a test is failing nondeterministically in CI, we consider that to
be an urgent problem.
* If the tests become a lot slower, that is also an urgent problem.
* Everything we do in CI should also have a way to run it quickly
(under 1 minute, preferably under 3 seconds), in order to iterate fast
in development. Except when working on the CI configuration itself, a
developer should never have to repeatedly wait 10 minutes for a full CI
run to iteratively debug something.

## CircleCI

### Useful debugging tips and tools

* Zulip uses the `ts` tool to log the current time on every line of the output in
our Travis CI scripts.  You can use this output to determine which steps are
actually consuming a lot of time.

* You can [sign up your personal repo for CircleCI][circleci-setup] so
that every remote branch you push will be tested, which can be helpful
when debugging something complicated.

* With your personal repo signed up, CircleCI
[allows you to SSH][circleci-ssh] into the job container if a job
fails. SSHing into the containers can be helpful, especially in rare
cases where the tests are passing in your computer but failing in the
CI. Make sure that you have uploaded your SSH keys to GitHub: CircleCI
uses those SSH keys for authentication.

[docker-hub]: https://hub.docker.com/
[circleci-setup]: ../git/cloning.html#step-3-configure-continuous-integration-for-your-fork
[circleci-ssh]: https://circleci.com/docs/2.0/ssh-access-jobs/

### Suites

The main CircleCI configuration file is
[./circleci/config.yml](https://github.com/zulip/zulip/blob/master/.circleci/config.yml).
We currently run several jobs during a CircleCI build. They are:
* trusty-python-3.4
* xenial-python-3.5
* bionic-python-3.6

Each runs the Zulip backend test suites, using the indicated
platform/OS and Python version. `bionic-python-3.6` job for example
runs the tests in Ubuntu Xenial with Python 3.6 pre-installed.
Additionally, the `xenial` suite also runs the Zulip frontend test
suites; since those are not platform-dependent, it doesn't make sense
to run them on all platforms.  Your build for the PR will pass only if
all the 3 jobs are executed successfully.

### Configuration

The remaining details in this section are primarily relevant for doing
development on our CI system and/or provisioning process.

The first key of the job section is `docker`. The docker key specifies
the image CircleCI should get from [Docker Hub][docker-hub] for running
the job. Once CircleCI fetches the image from Docker Hub, it will spin
up a docker container. See [images](#images) section to know more about
the images we use in CircleCI for testing.

After booting the container from the configured image, CircleCI will
create the directory mentioned in `working_directory` and all the
steps are be run from here.

The `steps` section describes describes everything: fetching the Zulip
code, provisioning, fetching catched data, running tests and uploading
coverage reports. The steps with prefix `*` reference aliases, which
are defined in the `aliases` section at the top of the file.

### Images

CircleCI tests are run in containers that are spun off from the images
maintained by Zulip team. The Dockerfiles for the various images can be
generated by running `./tools/circleci/generate-dockerfiles`. This command
will generate the Dockerfiles of the three Ubuntu releases in
`./tools/circleci/images/{release_name}` directories. Take a look at
`./tools/circleci/images.yml` to see how the Dockerfiles for the three
releases differ from each other. To further generate images from the
Dockerfiles and upload it to Docker Hub follow the instructions in the
generated Dockerfiles.

### Performance optimizations

#### Caching

An important element of making CircleCI perform effectively is
caching the provisioning of a Zulip development environment. In
particular, we cache the following.:

* Python virtualenvs
* node_modules directories

This has a huge impact on the performance of running tests in CircleCI
CI; without these caches, the average test time would be several times
longer.

We have designed these caches carefully (they are also used in
production and the Zulip development environment) to ensure that each
is named by a hash of its dependencies and ubuntu distribution name,
so Zulip should always be using the same version of dependencies it
would have used had the cache not existed.  In practice, bugs are
always possible, so be mindful of this possibility.

A consequence of this caching is that test jobs for branches which
modify `package.json`, `requirements/`, and other key dependencies
will be significantly slower than normal, because they won't get to
benefit from the cache.

## Travis CI

### Configuration

The main Travis configuration file is
[.travis.yml](https://github.com/zulip/zulip/blob/master/.travis.yml).
The specific test suites we have are listed in the `matrix` section,
which has a matrix of Python versions and test suites (`$TEST_SUITE`).

Currently there is only the production test suite in this section as we
have moved the backend and frontend suite to CircleCI. So the value of
the variable `$TEST_SUITE` would be always `production`.

We've configured it to use a few helper scripts for each job:

* `tools/ci/setup-$TEST_SUITE`: This script sets up the test
  environment for the production suite. This is a complicated process
  because of all the packages Travis installs.  See the comments in
  `tools/ci/setup-production` for details.
* `tools/ci/$TEST_SUITE`: The script that runs the actual test
  production test suite.

The main purpose of the distinction between the two is that if the
`setup-production` job fails, Travis CI will report it as the suite
having "Errored" (grey in their emails), whereas if the `production` job
fails, it'll be reported as "Failed" failure (red in their emails).
Note that Travis CI's web UI seems to make no visual distinction
between these.

An important detail is that Travis CI will by default hide most phases
other than the actual test; you can see this easily by looking at the
line numbers in the Travis CI output.  There are actually a bunch of
phases (e.g. the project's setup job, downloading caches near the
beginning, uploading caches at the end, etc.), and if you're debugging
our configuration, you'll want to look at these closely.

### Useful debugging tips and tools

* Zulip uses the `ts` tool to log the current time on every line of
  the output in our Travis CI scripts.  You can use this output to
  determine which steps are actually consuming a lot of time.

* For performance issues,
  [this statistics tool](https://scribu.github.io/travis-stats/#zulip/zulip/master)
  can give you test runtime history data that can help with
  determining when a performance issue was introduced and whether it
  was fixed.  Note you need to click the "Run" button for it to do
  anything.

* You can [sign up your personal repo for Travis CI][travis-fork] so
  that every remote branch you push will be tested, which can be
  helpful when debugging something complicated.

[travis-fork]: ../git/cloning.html#step-3-configure-continuous-integration-for-your-fork

### Performance optimizations

#### Caching

We cache the following as well apart from what is mentioned in CircleCI
caching section.

* Built/downloaded emoji sprite sheets and data.

This is probably worth eventually adding to the CircleCI caches, but
because it only saves ~5s, it hasn't been a priority yet.

#### Uninstalling packages

In the production suite, we run `apt-get upgrade` at some point
(effectively, because the Zulip installer does).  This carries a huge
performance cost in Travis CI, because (1) they don't keep their test
systems up to date and (2) literally everything is installed in their
build workers (e.g. several copies of Postgres, Java, MySQL, etc.).

In order to make Zulip's tests performance reasonably well, we
uninstall (or mark with `apt-mark hold`) many of these dependencies
that are irrelevant to Zulip in
[`tools/ci/setup-production`][setup-production].

[setup-production]: https://github.com/zulip/zulip/blob/master/tools/ci/setup-production