[#812] Guarantee a minimum of 0.5 CPUs to our DockerCLIOperator jobs

We also limit the memory usage to 350 MB. We were facing a few containers
starving, so I'm hoping these changes will fix that. I haven't added resource
limits to the "main" containers as well (worker, webserver, etc.) because I
couldn't find out how to do that in the Docker Cloud stack file.

opentrials/opentrials#812

dags/operators/docker_cli_operator.py

@@ -73,11 +73,17 @@ def _get_docker_run_command(self):
             for key, value in self.environment.items()
             if value is not None
         ]
+        resource_limits_params = [
+            '--memory=350m',
+            '--cpu-period=100000',
+            '--cpu-quota=50000',
+        ]
 
         docker_command = [
             'docker',
             'run',
             '--rm',
+        ] + resource_limits_params + [
         ] + env_params + [
             self.image,
             self.command,

tests/dags/operators/test_docker_cli_operator.py

@@ -4,6 +4,7 @@
     import mock
 import collections
 import io
+import re
 import shlex
 import subprocess
 import pytest
@@ -102,11 +103,13 @@ def test_get_docker_run_command_works_without_environment(self):
 
         docker_command = operator._get_docker_run_command()
 
-        assert docker_command == 'docker run --rm {image} {command}'.format(
+        command_regexp = r'docker run --rm.* {image} {command}'.format(
             image=operator.image,
             command=operator.command
         )
 
+        assert re.match(command_regexp, docker_command, re.IGNORECASE)
+
     def test_get_docker_run_command_works_with_environment(self):
         environment = collections.OrderedDict([
             ('foo', 'bar baz'),
@@ -122,10 +125,11 @@ def test_get_docker_run_command_works_with_environment(self):
 
         docker_command = operator._get_docker_run_command()
 
-        assert docker_command == 'docker run --rm --env "foo=$foo" --env "bar=$bar" {image} {command}'.format(
+        command_regexp = r'^docker run --rm.* --env "foo=\$foo" --env "bar=\$bar".* {image} {command}$'.format(
             image=operator.image,
             command=operator.command
         )
+        assert re.match(command_regexp, docker_command, re.IGNORECASE)
 
     @mock.patch('dags.operators.docker_cli_operator.DockerCLIOperator._run_command')
     def test_pull_image_runs_the_correct_command(self, run_command_mock):