README.md

# gitlab-workhorse

Gitlab-workhorse is a smart reverse proxy for GitLab. It handles
"large" HTTP requests such as file downloads, file uploads, Git
push/pull and Git archive downloads.

## Features that rely on Workhorse

Workhorse itself is not a feature, but there are several features in
GitLab that would not work efficiently without Workhorse.

To put the efficiency benefit in context, consider that in 2020Q3 on GitLab.com [we see][thanos] Rails application threads using on average about 200MB of RSS vs about 200KB for Workhorse goroutines.

[thanos]: https://thanos-query.ops.gitlab.net/graph?g0.range_input=1h&g0.max_source_resolution=0s&g0.expr=sum(ruby_process_resident_memory_bytes%7Bapp%3D%22webservice%22%2Cenv%3D%22gprd%22%2Crelease%3D%22gitlab%22%7D)%20%2F%20sum(puma_max_threads%7Bapp%3D%22webservice%22%2Cenv%3D%22gprd%22%2Crelease%3D%22gitlab%22%7D)&g0.tab=1&g1.range_input=1h&g1.max_source_resolution=0s&g1.expr=sum(go_memstats_sys_bytes%7Bapp%3D%22webservice%22%2Cenv%3D%22gprd%22%2Crelease%3D%22gitlab%22%7D)%2Fsum(go_goroutines%7Bapp%3D%22webservice%22%2Cenv%3D%22gprd%22%2Crelease%3D%22gitlab%22%7D)&g1.tab=1

Examples of features that rely on Workhorse:

### 1. `git clone` and `git push` over HTTP

Git clone, pull and push are slow because they transfer large amounts
of data and because each is CPU intensive on the GitLab side. Without
workhorse, HTTP access to Git repositories would compete with regular
web access to the application, requiring us to run way more Rails
application servers.

### 2. CI runner long polling

GitLab CI runners fetch new CI jobs by polling the GitLab server.
Workhorse acts as a kind of "waiting room" where CI runners can sit
and wait for new CI jobs. Because of Go's efficiency we can fit a lot
of runners in the waiting room at little cost. Without this waiting
room mechanism we would have to add a lot more Rails server capacity.

### 3. File uploads and downloads

File uploads and downloads may be slow either because the file is
large or because the user's connection is slow. Workhorse can handle
the slow part for Rails. This improves the efficiency of features such
as CI artifacts, package repositories, LFS objects, etc.

### 4. Websocket proxying

Features such as the web terminal require a long lived connection
between the user's web browser and a container inside GitLab that is
not directly accessible from the internet. Dedicating a Rails
application thread to proxying such a connection would cost much more
memory than it costs to have Workhorse look after it.

## Quick facts (how does Workhorse work)

-   Workhorse can handle some requests without involving Rails at all:
    for example, JavaScript files and CSS files are served straight
    from disk.
-   Workhorse can modify responses sent by Rails: for example if you use
    `send_file` in Rails then gitlab-workhorse will open the file on
    disk and send its contents as the response body to the client.
-   Workhorse can take over requests after asking permission from Rails.
    Example: handling `git clone`.
-   Workhorse can modify requests before passing them to Rails. Example:
    when handling a Git LFS upload Workhorse first asks permission from
    Rails, then it stores the request body in a tempfile, then it sends
    a modified request containing the tempfile path to Rails.
-   Workhorse can manage long-lived WebSocket connections for Rails.
    Example: handling the terminal websocket for environments.
-   Workhorse does not connect to Postgres, only to Rails and (optionally) Redis.
-   We assume that all requests that reach Workhorse pass through an
    upstream proxy such as NGINX or Apache first.
-   Workhorse does not accept HTTPS connections.
-   Workhorse does not clean up idle client connections.
-   We assume that all requests to Rails pass through Workhorse.

For more information see ['A brief history of
gitlab-workhorse'][brief-history-blog].

## Configuring Workhorse

For historical reasons Workhorse uses both command line flags, a configuration file and environment variables.

All new configuration options that get added to Workhorse should go into the configuration file.

## Usage

```
  gitlab-workhorse [OPTIONS]

Options:
  -apiCiLongPollingDuration duration
      Long polling duration for job requesting for runners (default 50s - enabled) (default 50ns)
  -apiLimit uint
      Number of API requests allowed at single time
  -apiQueueDuration duration
      Maximum queueing duration of requests (default 30s)
  -apiQueueLimit uint
      Number of API requests allowed to be queued
  -authBackend string
      Authentication/authorization backend (default "http://localhost:8080")
  -authSocket string
      Optional: Unix domain socket to dial authBackend at
  -cableBackend string
      Optional: ActionCable backend (default authBackend)
  -cableSocket string
      Optional: Unix domain socket to dial cableBackend at (default authSocket)
  -config string
      TOML file to load config from
  -developmentMode
      Allow the assets to be served from Rails app
  -documentRoot string
      Path to static files content (default "public")
  -listenAddr string
      Listen address for HTTP server (default "localhost:8181")
  -listenNetwork string
      Listen 'network' (tcp, tcp4, tcp6, unix) (default "tcp")
  -listenUmask int
      Umask for Unix socket
  -logFile string
      Log file location
  -logFormat string
      Log format to use defaults to text (text, json, structured, none) (default "text")
  -pprofListenAddr string
      pprof listening address, e.g. 'localhost:6060'
  -prometheusListenAddr string
      Prometheus listening address, e.g. 'localhost:9229'
  -proxyHeadersTimeout duration
      How long to wait for response headers when proxying the request (default 5m0s)
  -secretPath string
      File with secret key to authenticate with authBackend (default "./.gitlab_workhorse_secret")
  -version
      Print version and exit
```

The 'auth backend' refers to the GitLab Rails application. The name is
a holdover from when gitlab-workhorse only handled Git push/pull over
HTTP.

Gitlab-workhorse can listen on either a TCP or a Unix domain socket. It
can also open a second listening TCP listening socket with the Go
[net/http/pprof profiler server](http://golang.org/pkg/net/http/pprof/).

Gitlab-workhorse can listen on redis events (currently only builds/register
for runners). This requires you to pass a valid TOML config file via
`-config` flag.
For regular setups it only requires the following (replacing the string
with the actual socket)

### Redis

Gitlab-workhorse integrates with Redis to do long polling for CI build
requests. This is configured via two things:

-   Redis settings in the TOML config file
-   The `-apiCiLongPollingDuration` command line flag to control polling
    behavior for CI build requests

It is OK to enable Redis in the config file but to leave CI polling
disabled; this just results in an idle Redis pubsub connection. The
opposite is not possible: CI long polling requires a correct Redis
configuration.

Below we discuss the options for the `[redis]` section in the config
file.

```
[redis]
URL = "unix:///var/run/gitlab/redis.sock"
Password = "my_awesome_password"
Sentinel = [ "tcp://sentinel1:23456", "tcp://sentinel2:23456" ]
SentinelMaster = "mymaster"
```

- `URL` takes a string in the format `unix://path/to/redis.sock` or
`tcp://host:port`.
- `Password` is only required if your redis instance is password-protected
- `Sentinel` is used if you are using Sentinel.
  *NOTE* that if both `Sentinel` and `URL` are given, only `Sentinel` will be used

Optional fields are as follows:
```
[redis]
DB = 0
ReadTimeout = "1s"
KeepAlivePeriod = "5m"
MaxIdle = 1
MaxActive = 1
```

- `DB` is the Database to connect to. Defaults to `0`
- `ReadTimeout` is how long a redis read-command can take. Defaults to `1s`
- `KeepAlivePeriod` is how long the redis connection is to be kept alive without anything flowing through it. Defaults to `5m`
- `MaxIdle` is how many idle connections can be in the redis-pool at once. Defaults to 1
- `MaxActive` is how many connections the pool can keep. Defaults to 1

### Relative URL support

If you are mounting GitLab at a relative URL, e.g.
`example.com/gitlab`, then you should also use this relative URL in
the `authBackend` setting:

```
gitlab-workhorse -authBackend http://localhost:8080/gitlab
```

### Interaction of authBackend and authSocket

The interaction between `authBackend` and `authSocket` can be a bit
confusing. It comes down to: if `authSocket` is set it overrides the
_host_ part of `authBackend` but not the relative path.

In table form:

|authBackend|authSocket|Workhorse connects to?|Rails relative URL|
|---|---|---|---|
|unset|unset|`localhost:8080`|`/`|
|`http://localhost:3000`|unset|`localhost:3000`|`/`|
|`http://localhost:3000/gitlab`|unset|`localhost:3000`|`/gitlab`|
|unset|`/path/to/socket`|`/path/to/socket`|`/`|
|`http://localhost:3000`|`/path/to/socket`|`/path/to/socket`|`/`|
|`http://localhost:3000/gitlab`|`/path/to/socket`|`/path/to/socket`|`/gitlab`|

The same applies to `cableBackend` and `cableSocket`.

## Installation

To install gitlab-workhorse you need [Go 1.13 or
newer](https://golang.org/dl) and [GNU
Make](https://www.gnu.org/software/make/).

To install into `/usr/local/bin` run `make install`.

```
make install
```

To install into `/foo/bin` set the PREFIX variable.

```
make install PREFIX=/foo
```

On some operating systems, such as FreeBSD, you may have to use
`gmake` instead of `make`.

## Dependencies

### Exiftool

Workhorse uses [exiftool](https://www.sno.phy.queensu.ca/~phil/exiftool/) for
removing EXIF data (which may contain sensitive information) from uploaded
images. If you installed GitLab:

-   Using the Omnibus package, you're all set.
    *NOTE* that if you are using CentOS Minimal, you may need to install `perl`
    package: `yum install perl`
-   From source, make sure `exiftool` is installed:

    ```sh
    # Debian/Ubuntu
    sudo apt-get install libimage-exiftool-perl

    # RHEL/CentOS
    sudo yum install perl-Image-ExifTool
    ```

## Error tracking

GitLab-Workhorse supports remote error tracking with
[Sentry](https://sentry.io). To enable this feature set the
`GITLAB_WORKHORSE_SENTRY_DSN` environment variable.
You can also set the `GITLAB_WORKHORSE_SENTRY_ENVIRONMENT` environment variable to
use the Sentry environment functionality to separate staging, production and
development.

Omnibus (`/etc/gitlab/gitlab.rb`):

```
gitlab_workhorse['env'] = {
    'GITLAB_WORKHORSE_SENTRY_DSN' => 'https://foobar'
    'GITLAB_WORKHORSE_SENTRY_ENVIRONMENT' => 'production'
}
```

Source installations (`/etc/default/gitlab`):

```
export GITLAB_WORKHORSE_SENTRY_DSN='https://foobar'
export GITLAB_WORKHORSE_SENTRY_ENVIRONMENT='production'
```

## Tests

Run the tests with:

```
make clean test
```

### Coverage / what to test

Each feature in gitlab-workhorse should have an integration test that
verifies that the feature 'kicks in' on the right requests and leaves
other requests unaffected. It is better to also have package-level tests
for specific behavior but the high-level integration tests should have
the first priority during development.

It is OK if a feature is only covered by integration tests.

## Distributed Tracing

Workhorse supports distributed tracing through [LabKit][] using [OpenTracing APIs](https://opentracing.io).

By default, no tracing implementation is linked into the binary, but different OpenTracing providers can be linked in using [build tags][build-tags]/[build constraints][build-tags]. This can be done by setting the `BUILD_TAGS` make variable.

For more details of the supported providers, see LabKit, but as an example, for Jaeger tracing support, include the tags: `BUILD_TAGS="tracer_static tracer_static_jaeger"`.

```shell
make BUILD_TAGS="tracer_static tracer_static_jaeger"
```

Once Workhorse is compiled with an opentracing provider, the tracing configuration is configured via the `GITLAB_TRACING` environment variable.

For example:

```shell
GITLAB_TRACING=opentracing://jaeger ./gitlab-workhorse
```

## Continuous Profiling

Workhorse supports continuous profiling through [LabKit][] using [Stackdriver Profiler](https://cloud.google.com/profiler).

By default, the Stackdriver Profiler implementation is linked in the binary using [build tags][build-tags], though it's not
required and can be skipped.

For example:

```shell
make BUILD_TAGS=""
```

Once Workhorse is compiled with Continuous Profiling, the profiler configuration can be set via `GITLAB_CONTINUOUS_PROFILING`
environment variable.

For example:

```shell
GITLAB_CONTINUOUS_PROFILING="stackdriver?service=workhorse&service_version=1.0.1&project_id=test-123 ./gitlab-workhorse"
```

More information about see the [LabKit monitoring docs](https://gitlab.com/gitlab-org/labkit/-/blob/master/monitoring/doc.go).

## License

This code is distributed under the MIT license, see the [LICENSE](LICENSE) file.

[brief-history-blog]: https://about.gitlab.com/2016/04/12/a-brief-history-of-gitlab-workhorse/
[LabKit]: https://gitlab.com/gitlab-org/labkit/
[build-tags]: https://golang.org/pkg/go/build/#hdr-Build_Constraints