You can debug your plugin in a running TeamCity just like a regular Java application debug: start TeamCity server with debug-enabling JVM options and then connect to a remote debug port from the IDE. If you start TeamCity server from outside of your IDE, in IntelliJ IDE you can use "Remote" run configuration, check related external blog post. The JVM options for the server can be set via TEAMCITY_SERVER_OPTS environment variable.
Since TeamCity 2018.2, you can update your plugin without the server restart.
To enable TeamCity development mode, pass the
teamcity.development.mode=true internal property. Using the option you will:
Enforce application server to quicker recompile changed
Disable JS and CSS resources merging/caching
In the plugin descriptor, set the
allow-runtime-reload="true" parameters for deployment.
In versions prior to 2018.2, shut down the server, update the plugin, and start the server again; or use the following hints to eliminate the server restart in the certain cases:
if you do not change code affecting plugin initialization and change only body of the methods, you can attach to the server process with a debugger and use Java hotswap to reload the changed classes from your IDE without web server restart. Note that the standard hotswap does not allow you to change method signatures.
if you make a change in some resource (jsp, js, images) you can copy the resources to
webapps/ROOT/plugins/<plugin-name>directory to allow Tomcat to reload them.
change in build agent part of plugin will initiate build agents upgrade.
If you replace a deployed plugin
.zip file with changed class files while TeamCity server is running, this can lead to the
NoClassDefFound errors. To avoid this, set the
teamcity.development.shadowCopyClasses=true internal property.
This will result in:
.teamcity_shadow" directory for each plugin .jar file;
avoiding .jar files update on changing the plugin archive.