In addition to the main server, you can start a secondary TeamCity server looking at the same database and data directory as the main one.
In TeamCity 2018.1 the secondary server works provides user interface in the read-only mode onlyand does not perform any other background activity.
With secondary node it is possible to set up a High-Availability TeamCity installation that will have zero read downtime, i.e. when the main server is unavailable or is performing an upgrade, requests will be routed to the secondary node. Such setup requires installing both the main server and the secondary node behind a reverse proxy that should be configured to route requests to the main server while it's available and to the secondary one in other cases.
In TeamCity 2018.2 the secondary server can work provides user interface in the read-only mode and in the can optionally perform VCS repositories polling mode.
The sections below detail describes the secondary node and proxy configuration.
Secondary Node Overview
The same TeamCity server distribution is used for the main and secondary nodes. The primary setup is running the two server nodes on different machines.
The secondary node in a High-Availability setup uses the license from the main server and does not require a separate license.
When a TeamCity server is started as the secondary node, it allows users read operations: view the build information, download artifacts, etc. during the downtime of the main server, e.g. during upgrade. When both main and secondary nodes are active, the secondary node constantly watches for different events produced by the main server and refreshes its internal state. So users whould see actual state on the secondary node at any point of time.
It is recommended that both the main TeamCity server and the secondary node should be of have the exactly the same version. However, the main server and the secondary one can be running different versions when the main server is upgraded. See the Upgrade section below.
The secondary node does not allow changing the server configuration, therefore not all the pages in the Administration area are available.start builds, or change state of the server anyhow. Therefore the pages are served in the read only mode, and not all the Administration area pages are available. There are no actions like Run build, etc.
Currently, only bundled and a limited set of some other plugins are loaded by the secondary server, so some functionality provided by external plugins can be missing.
Users may need to re-login when they are routed to the secondary node if they didn't use Remember Me.