Exposed Services and Ports

Jenkins is a fairly complex application and as such does more than just serve a web interface. This section documents the services it frequently exposes on the network.

Plugins may expose further services on the network. Only very commonly installed plugins are considered below.

Web UI

The web UI served via HTTP (or HTTPS), by default on port 8080. Sometimes Jenkins is running behind a reverse proxy that may customize or filter requests and responses.

For an overview of the URLs accessible to users without any permissions in Jenkins, see Access Control.

TCP Agent Listener Port

Jenkins can expose a TCP port that allows inbound agents to connect to it. It can be enabled, disabled, and configured in Manage Jenkins » Configure Global Security.

The two supported modes (while enabled) are:

  1. Random: The TCP port is chosen at random to avoid collisions on the Jenkins controller. The downside to randomized ports is that they are chosen during the boot of the Jenkins controller, making it difficult to manage firewall rules allowing TCP traffic.

  2. Fixed: The port is chosen by the Jenkins administrator and is consistent across reboots of the Jenkins controller. This makes it easier to manage firewall rules allowing TCP-based agents to connect to the controller.

This service is disabled by default in most packages, but the Docker images expose it at port 50000.

HTTP requests at this port get a minimal plain text response with some diagnostic information. It looks like the following:

Jenkins-Agent-Protocols: JNLP4-connect, Ping (1)
Jenkins-Version: 2.289 (2)
Jenkins-Session: b4783dfa (3)
Client: 172.17.0.1 (4)
Server: 172.17.0.3 (5)
Remoting-Minimum-Version: 3.14 (6)
1 List of currently enabled TCP inbound agent protocols.
2 The current version of Jenkins.
3 The session of the current Jenkins execution. This is unrelated to web session cookies. This is changed to a new value whenever Jenkins starts. It is used in various URLs to help implement caching of static resources, and can be used by clients to tell whether Jenkins restarted.
4 The client IP address as seen from Jenkins.
5 The Jenkins controller’s IP address.
6 The minimum required version of the Remoting library for agents to connect to this Jenkins controller.

Inbound agents may instead be configured to use WebSocket transport to connect to Jenkins. In this case no extra TCP port need be enabled and no special security configuration is needed.

SSH Server

The SSH Server Plugin can be configured to open an SSH port on the Jenkins controller.

This plugin’s functionality was part of Jenkins (core) until Jenkins 2.281.

Authentication can be username/password or using public key authentication. For the latter, the public keys can be stored in Jenkins users' profiles.

This SSH server does not provide a regular OS shell once logged in. Instead, it provides a shell-like interface for the Jenkins CLI.

Additionally, some plugins may provide features that require the SSH server to be enabled, like the GIT server Plugin.

This service is disabled by default.

UDP and mDNS Service Discovery

Jenkins releases 2.219 and earlier included features that allowed users to discover Jenkins on their network. These features have been removed without replacement in Jenkins 2.220 for security reasons.