Enable overriding environment detection (#60)

Sometimes it would be great to override the default selected environment (e.g. to force usage of the Lambda environment outside of Lambda), which this change enables.

The code is based on #26.

aws_embedded_metrics/config/configuration.py

@@ -11,6 +11,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from typing import Optional
+
 
 class Configuration:
     def __init__(
@@ -24,6 +26,7 @@ def __init__(
         ec2_metadata_endpoint: str = None,
         namespace: str = None,
         disable_metric_extraction: bool = False,
+        environment: Optional[str] = None,
     ):
         self.debug_logging_enabled = debug_logging_enabled
         self.service_name = service_name
@@ -34,3 +37,4 @@ def __init__(
         self.ec2_metadata_endpoint = ec2_metadata_endpoint
         self.namespace = namespace
         self.disable_metric_extraction = disable_metric_extraction
+        self.environment = environment

aws_embedded_metrics/config/environment_configuration_provider.py

@@ -25,6 +25,7 @@
 EC2_METADATA_ENDPOINT = "EC2_METADATA_ENDPOINT"
 NAMESPACE = "NAMESPACE"
 DISABLE_METRIC_EXTRACTION = "DISABLE_METRIC_EXTRACTION"
+ENVIRONMENT_OVERRIDE = "ENVIRONMENT"
 
 
 class EnvironmentConfigurationProvider:
@@ -43,6 +44,7 @@ def get_configuration(self) -> Configuration:
             self.__get_env_var(EC2_METADATA_ENDPOINT),
             self.__get_env_var(NAMESPACE),
             self.__get_bool_env_var(DISABLE_METRIC_EXTRACTION),
+            self.__get_env_var(ENVIRONMENT_OVERRIDE),
         )
 
     @staticmethod

aws_embedded_metrics/environment/environment_detector.py

@@ -12,6 +12,7 @@
 # limitations under the License.
 
 import logging
+from aws_embedded_metrics import config
 from aws_embedded_metrics.environment import Environment
 from aws_embedded_metrics.environment.default_environment import DefaultEnvironment
 from aws_embedded_metrics.environment.lambda_environment import LambdaEnvironment
@@ -20,7 +21,11 @@
 
 log = logging.getLogger(__name__)
 
-environments = [LambdaEnvironment(), EC2Environment()]
+lambda_environment = LambdaEnvironment()
+ec2_environment = EC2Environment()
+default_environment = DefaultEnvironment()
+environments = [lambda_environment, ec2_environment]
+Config = config.get_config()
 
 
 class EnvironmentCache:
@@ -32,6 +37,19 @@ async def resolve_environment() -> Environment:
         log.debug("Environment resolved from cache.")
         return EnvironmentCache.environment
 
+    if Config.environment:
+        lower_configured_enviroment = Config.environment.lower()
+        if lower_configured_enviroment == "lambda":
+            EnvironmentCache.environment = lambda_environment
+        elif lower_configured_enviroment == "ec2":
+            EnvironmentCache.environment = ec2_environment
+        elif lower_configured_enviroment == "default":
+            EnvironmentCache.environment = default_environment
+        else:
+            log.info("Failed to understand environment override: %s", Config.environment)
+    if EnvironmentCache.environment is not None:
+        return EnvironmentCache.environment
+
     for env_under_test in environments:
         is_environment = False
         try:
@@ -49,5 +67,5 @@ async def resolve_environment() -> Environment:
             return env_under_test
 
     log.info("No environment was detected. Using default.")
-    EnvironmentCache.environment = DefaultEnvironment()
+    EnvironmentCache.environment = default_environment
     return EnvironmentCache.environment

tests/config/test_config.py

@@ -24,6 +24,7 @@ def test_can_get_config_from_environment(monkeypatch):
     ec2_metadata_endpoint = fake.word()
     namespace = fake.word()
     disable_metric_extraction = True
+    environment_override = fake.word()
 
     monkeypatch.setenv("AWS_EMF_ENABLE_DEBUG_LOGGING", str(debug_enabled))
     monkeypatch.setenv("AWS_EMF_SERVICE_NAME", service_name)
@@ -34,6 +35,7 @@ def test_can_get_config_from_environment(monkeypatch):
     monkeypatch.setenv("AWS_EMF_EC2_METADATA_ENDPOINT", ec2_metadata_endpoint)
     monkeypatch.setenv("AWS_EMF_NAMESPACE", namespace)
     monkeypatch.setenv("AWS_EMF_DISABLE_METRIC_EXTRACTION", str(disable_metric_extraction))
+    monkeypatch.setenv("AWS_EMF_ENVIRONMENT", environment_override)
 
     # act
     result = get_config()
@@ -48,6 +50,7 @@ def test_can_get_config_from_environment(monkeypatch):
     assert result.ec2_metadata_endpoint == ec2_metadata_endpoint
     assert result.namespace == namespace
     assert result.disable_metric_extraction == disable_metric_extraction
+    assert result.environment == environment_override
 
 
 def test_can_override_config(monkeypatch):
@@ -61,6 +64,7 @@ def test_can_override_config(monkeypatch):
     monkeypatch.setenv("AWS_EMF_EC2_METADATA_ENDPOINT", fake.word())
     monkeypatch.setenv("AWS_EMF_NAMESPACE", fake.word())
     monkeypatch.setenv("AWS_EMF_DISABLE_METRIC_EXTRACTION", str(True))
+    monkeypatch.setenv("AWS_EMF_ENVIRONMENT", fake.word())
 
     config = get_config()
 
@@ -73,6 +77,7 @@ def test_can_override_config(monkeypatch):
     ec2_metadata_endpoint = fake.word()
     namespace = fake.word()
     disable_metric_extraction = False
+    environment = fake.word()
 
     # act
     config.debug_logging_enabled = debug_enabled
@@ -84,6 +89,7 @@ def test_can_override_config(monkeypatch):
     config.ec2_metadata_endpoint = ec2_metadata_endpoint
     config.namespace = namespace
     config.disable_metric_extraction = disable_metric_extraction
+    config.environment = environment
 
     # assert
     assert config.debug_logging_enabled == debug_enabled
@@ -95,3 +101,4 @@ def test_can_override_config(monkeypatch):
     assert config.ec2_metadata_endpoint == ec2_metadata_endpoint
     assert config.namespace == namespace
     assert config.disable_metric_extraction == disable_metric_extraction
+    assert config.environment == environment

tests/environment/test_environment_detector.py

@@ -3,15 +3,14 @@
 import pytest
 from importlib import reload
 
-from aws_embedded_metrics.config import get_config
+from aws_embedded_metrics import config
 from aws_embedded_metrics.environment.lambda_environment import LambdaEnvironment
 from aws_embedded_metrics.environment.default_environment import DefaultEnvironment
 
 from aws_embedded_metrics.environment import ec2_environment
 from aws_embedded_metrics.environment import environment_detector
 
 fake = Faker()
-Config = get_config()
 
 
 @pytest.fixture
@@ -60,3 +59,31 @@ async def test_resolve_environment_returns_default_envionment(before):
 
     # assert
     assert isinstance(result, DefaultEnvironment)
+
+
+@pytest.mark.asyncio
+async def test_resolve_environment_returns_override_ec2(before, monkeypatch):
+    # arrange
+    monkeypatch.setenv("AWS_EMF_ENVIRONMENT", "ec2")
+    reload(config)
+    reload(environment_detector)
+
+    # act
+    result = await environment_detector.resolve_environment()
+
+    # assert
+    assert isinstance(result, ec2_environment.EC2Environment)
+
+
+@pytest.mark.asyncio
+async def test_resolve_environment_returns_override_lambda(before, monkeypatch):
+    # arrange
+    monkeypatch.setenv("AWS_EMF_ENVIRONMENT", "lambda")
+    reload(config)
+    reload(environment_detector)
+
+    # act
+    result = await environment_detector.resolve_environment()
+
+    # assert
+    assert isinstance(result, LambdaEnvironment)