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GitLab

Web terminals

Introduced in GitLab 8.15.

NOTE: Only project maintainers and owners can access web terminals.

With the introduction of the Kubernetes integration, GitLab gained the ability to store and use credentials for a Kubernetes cluster. One of the things it uses these credentials for is providing access to web terminals for environments.

How it works

A detailed overview of the architecture of web terminals and how they work can be found in this document. In brief:

  • GitLab relies on the user to provide their own Kubernetes credentials, and to appropriately label the pods they create when deploying.
  • When a user navigates to the terminal page for an environment, they are served a JavaScript application that opens a WebSocket connection back to GitLab.
  • The WebSocket is handled in Workhorse, rather than the Rails application server.
  • Workhorse queries Rails for connection details and user permissions. Rails queries Kubernetes for them in the background using Sidekiq.
  • Workhorse acts as a proxy server between the user's browser and the Kubernetes API, passing WebSocket frames between the two.
  • Workhorse regularly polls Rails, terminating the WebSocket connection if the user no longer has permission to access the terminal, or if the connection details have changed.

Security

GitLab and GitLab Runner take some precautions to keep interactive web terminal data encrypted between them, and everything protected with authorization guards. This is described in more detail below.

  • Interactive web terminals are completely disabled unless [session_server] is configured.
  • Every time the runner starts, it generates an x509 certificate that is used for a wss (Web Socket Secure) connection.
  • For every created job, a random URL is generated which is discarded at the end of the job. This URL is used to establish a web socket connection. The URL for the session is in the format (IP|HOST):PORT/session/$SOME_HASH, where the IP/HOST and PORT are the configured listen_address.
  • Every session URL that is created has an authorization header that needs to be sent, to establish a wss connection.
  • The session URL is not exposed to the users in any way. GitLab holds all the state internally and proxies accordingly.

Enabling and disabling terminal support

NOTE: AWS Elastic Load Balancers (ELBs) do not support web sockets. AWS Application Load Balancers (ALBs) must be used if you want web terminals to work. See AWS Elastic Load Balancing Product Comparison for more information.

As web terminals use WebSockets, every HTTP/HTTPS reverse proxy in front of Workhorse needs to be configured to pass the Connection and Upgrade headers through to the next one in the chain. If you installed GitLab using Omnibus, or from source, starting with GitLab 8.15, this should be done by the default configuration, so there's no need for you to do anything.

However, if you run a load balancer in front of GitLab, you may need to make some changes to your configuration. These guides document the necessary steps for a selection of popular reverse proxies:

Workhorse doesn't let WebSocket requests through to non-WebSocket endpoints, so it's safe to enable support for these headers globally. If you'd rather had a narrower set of rules, you can restrict it to URLs ending with /terminal.ws (although this may still have a few false positives).

If you installed from source, or have made any configuration changes to your Omnibus installation before upgrading to 8.15, you may need to make some changes to your configuration. See the Upgrading Community Edition and Enterprise Edition from source document for more details.

If you'd like to disable web terminal support in GitLab, just stop passing the Connection and Upgrade hop-by-hop headers in the first HTTP reverse proxy in the chain. For most users, this is the NGINX server bundled with Omnibus GitLab, in which case, you need to:

  • Find the nginx['proxy_set_headers'] section of your gitlab.rb file
  • Ensure the whole block is uncommented, and then comment out or remove the Connection and Upgrade lines.

For your own load balancer, just reverse the configuration changes recommended by the above guides.

When these headers are not passed through, Workhorse returns a 400 Bad Request response to users attempting to use a web terminal. In turn, they receive a Connection failed message.

Limiting WebSocket connection time

Introduced in GitLab 8.17.

Terminal sessions, by default, do not expire. You can limit terminal session lifetime in your GitLab instance. To do so, navigate to Admin Area > Settings > Web terminal, and set a max session time.