feat: remove need to specify cpu_units

We not allocate sufficient cpu units to ensure distinct task
placement across the cluster without forcing the test plan to
take it into account.

Closes #20

ardere/aws.py

@@ -23,6 +23,45 @@
 with open(shell_path, 'r') as f:
     shell_script = f.read()
 
+# List tracking vcpu's of all instance types for cpu unit reservations
+# We are intentionally leaving out the following instance types as they're
+# considered overkill for load-testing purposes or any instance req's we have
+# experienced so far:
+#     P2, G2, F1, I3, D2
+ec2_vcpu_by_vcpu = {
+    1: ["t2.nano", "t2.micro", "t2.small", "m3.medium"],
+    2: ["t2.medium", "t2.large", "m3.large", "m4.large", "c3.large",
+        "c4.large", "r3.large", "r4.large"],
+    4: ["t2.xlarge", "m3.xlarge", "m4.xlarge", "c3.xlarge", "c4.xlarge",
+        "r3.xlarge", "r4.xlarge"],
+    8: ["t2.2xlarge", "m3.2xlarge", "m4.2xlarge", "c3.2xlarge", "c4.2xlarge",
+        "r3.2xlarge", "r4.2xlarge"],
+    16: ["m4.4xlarge", "c3.4xlarge", "c4.4xlarge", "r3.4xlarge", "r4.4xlarge"],
+    32: ["c3.8xlarge", "r3.8xlarge", "r4.8xlarge"],
+    36: ["c4.8xlarge"],
+    40: ["m4.10xlarge"],
+    64: ["m4.16xlarge", "x1.16xlarge", "r4.16xlarge"],
+    128: ["x1.32xlarge"]
+}
+
+# Build a list of vcpu's by instance type
+ec2_vcpu_by_type = {}
+for vcpu, instance_types in ec2_vcpu_by_vcpu.items():
+    for instance_type in instance_types:
+        ec2_vcpu_by_type[instance_type] = vcpu
+
+
+def cpu_units_for_instance_type(instance_type):
+    """Calculate how many CPU units to allocate for an instance_type
+
+    We calculate cpu_units as 1024 * vcpu's for each instance to allocate
+    almost the entirety of the instance's cpu units to the load-testing
+    container. We take out 512 to ensure some leftover capacity for other
+    utility containers we run with the load-testing container.
+
+    """
+    return (ec2_vcpu_by_type[instance_type] * 1024) - 512
+
 
 class ECSManager(object):
     """ECS Manager queries and manages an ECS cluster"""
@@ -165,7 +204,7 @@ def create_service(self, step):
                 {
                     "name": step["name"],
                     "image": step["container_name"],
-                    "cpu": step["cpu_units"],
+                    "cpu": cpu_units_for_instance_type(step["instance_type"]),
                     # using only memoryReservation sets no hard limit
                     "memoryReservation": 256,
                     "environment": env_vars,

tests/fixtures.py

@@ -9,7 +9,6 @@
       "instance_count": 1,
       "instance_type": "t2.medium",
       "run_max_time": 140,
-      "cpu_units": 2048,
       "environment_data": [
           "SOME_VAR=great-value"
       ],
@@ -26,7 +25,6 @@
     "instance_count": 1,
     "instance_type": "t2.medium",
     "run_max_time": 140,
-    "cpu_units": 2048,
     "container_name": "bbangert/pushgo:1.5rc4",
     "port_mapping": "8080:8090,8081:8081,3000:3000,8082:8082",
     "load_balancer": {

tests/test_aws.py

@@ -96,6 +96,10 @@ def test_create_service(self):
 
         eq_(step["serviceArn"], "arn:of:some:service::")
         ecs._ecs_client.register_task_definition.assert_called()
+        _, kwargs = ecs._ecs_client.register_task_definition.call_args
+        container_def = kwargs["containerDefinitions"][0]
+
+        eq_(container_def["cpu"], 1536)
 
     def test_create_services(self):
         ecs = self._make_FUT()