Managing Ports in Concurrently Running Tests

As of July, 2021, Geode's build system no longer executes test worker processes in separate Docker containers.

This means that each test worker JVM and each Java process started by a test executes directly in the environment provided by the host machine. This creates a risk that tests running concurrently might try to bind to the same port.

To reduce this risk, Gradle now assigns each test worker JVM a distinct range of membership ports and a distinct range of non-membership ports. No two concurrently executing tests will have any ports in common. In CI, which runs 24 distributed tests concurrently, each test gets a range of about 400 membership ports and 800 non-membership ports.

In JVMs running the latest version of Geode, AvailablePort and AvailablePortHelper will choose random ports from these assigned ranges. As a result, no two well-behaved tests will ever try to bind to the same port, no matter how many are running concurrently.

When you write a test, keep the following guidelines in mind, to make sure your test uses only the ranges of ports that Gradle assigned to it:

• To assign an available port, call AvailablePortHelper or AvailablePort. These are the only classes that know about the reduced port range for the test.
• Call AvailablePort and AvailablePortHelper only in the current version of Geode. Do not call these classes in Child VMs running older versions of Geode. Older versions of Geode do not honor the new, reduced port ranges.
• Do not launch any service using Geode’s default port for that service. Always explicitly assign an available port. The only safe use of default ports is in a test to verify that a service uses its default port by default.
• Do not launch any service using a port number hard-coded into the test. Always explicitly assign an available port. There is no safe use of any hard-coded port number in tests that can run concurrently.
• Do not attempt to reuse an ephemeral port. Some tests start a member on an ephemeral port, stop the member, and attempt to restart it on the same port. This is not safe. It was never safe. During the time between when the member stops and when it restarts, the port is available for the operating system to give to any other process. In CI, it is very, very likely that one or more concurrently-running tests (or other processes) will request ephemeral ports. If one of those processes gets the port your test was using, your test will fail.