automation: initial support for running Linux tests Building on top of our Windows automation support, this commit implements support for performing automated tasks on remote Linux machines. Specifically, we implement support for running tests on ephemeral EC2 instances. This seems to be a worthwhile place to start, as building packages on Linux is more or less a solved problem because we already have facilities for building in Docker containers, which provide "good enough" reproducibility guarantees. The new `run-tests-linux` command works similarly to `run-tests-windows`: it ensures an AMI with hg dependencies is available, provisions a temporary EC2 instance with this AMI, pushes local changes to that instance via SSH, then invokes `run-tests.py`. Using this new command, I am able to run the entire test harness substantially faster then I am on my local machine courtesy of access to massive core EC2 instances: wall: 16:20 ./run-tests.py -l (i7-6700K) wall: 14:00 automation.py run-tests-linux --ec2-instance c5.2xlarge wall: 8:30 automation.py run-tests-linux --ec2-instance m5.4xlarge wall: 8:04 automation.py run-tests-linux --ec2-instance c5.4xlarge wall: 4:30 automation.py run-tests-linux --ec2-instance c5.9xlarge wall: 3:57 automation.py run-tests-linux --ec2-instance m5.12xlarge wall: 3:05 automation.py run-tests-linux --ec2-instance m5.24xlarge wall: 3:02 automation.py run-tests-linux --ec2-instance c5.18xlarge ~3 minute wall time to run pretty much the entire test harness is not too bad! The AMIs install multiple versions of Python. And the run-tests-linux command specifies which one to use: automation.py run-tests-linux --python system3 automation.py run-tests-linux --python 3.5 automation.py run-tests-linux --python pypy2.7 By default, the system Python 2.7 is used. Using this functionality, I was able to identity some unexpected test failures on PyPy! Included in the feature is support for running with alternate filesystems. You can simply pass --filesystem to the command to specify the type of filesystem to run tests on. When the ephemeral instance is started, a new filesystem will be created and tests will run from it: wall: 4:30 automation.py run-tests-linux --ec2-instance c5.9xlarge wall: 4:20 automation.py run-tests-linux --ec2-instance c5d.9xlarge --filesystem xfs wall: 4:24 automation.py run-tests-linux --ec2-instance c5d.9xlarge --filesystem tmpfs wall: 4:26 automation.py run-tests-linux --ec2-instance c5d.9xlarge --filesystem ext4 We also support multiple Linux distributions: $ automation.py run-tests-linux --distro debian9 total time: 298.1s; setup: 60.7s; tests: 237.5s; setup overhead: 20.4% $ automation.py run-tests-linux --distro ubuntu18.04 total time: 286.1s; setup: 61.3s; tests: 224.7s; setup overhead: 21.4% $ automation.py run-tests-linux --distro ubuntu18.10 total time: 278.5s; setup: 58.2s; tests: 220.3s; setup overhead: 20.9% $ automation.py run-tests-linux --distro ubuntu19.04 total time: 265.8s; setup: 42.5s; tests: 223.3s; setup overhead: 16.0% Debian and Ubuntu are supported because those are what I use and am most familiar with. It should be easy enough to add support for other distros. Unlike the Windows AMIs, Linux EC2 instances bill per second. So the cost to instantiating an ephemeral instance isn't as severe. That being said, there is some overhead, as it takes several dozen seconds for the instance to boot, push local changes, and build Mercurial. During this time, the instance is largely CPU idle and wasting money. Even with this inefficiency, running tests is relatively cheap: $0.15-$0.25 per full test run. A machine running tests as efficiently as these EC2 instances would cost say $6,000, so you can run the test harness a >20,000 times for the cost of an equivalent machine. Running tests in EC2 is almost certainly cheaper than buying a beefy machine for developers to use :) # no-check-commit because foo_bar function names Differential Revision: https://phab.mercurial-scm.org/D6319