Add Sentry integration

Why these changes are being introduced:
We generally want Sentry integration for most apps, and its a bit
different for lambda functions than for other Python apps so it's
important to have an example integration in this lambda template repo.

How this addresses that need:
* Adds sentry_sdk dependency to Pipfile.
* Adds Sentry lambda integration to my_function module.
* Adds check for required WORKSPACE env in lambda_handler function.
* Adds tests for new functionality.
* Updates README to include instructions for setting up a Sentry
  project when creating a new app from this template.

Relevant ticket(s):
* https://mitlibraries.atlassian.net/browse/IN-526

Author: hakbailey

Pipfile

@@ -4,6 +4,7 @@ verify_ssl = true
 name = "pypi"
 
 [packages]
+sentry-sdk = "*"
 
 [dev-packages]
 bandit = "*"

README.md

@@ -15,6 +15,10 @@ A template repository for creating Python lambda functions.
       - Dependabot alerts
       - Dependabot security updates
       - Secret scanning
+7. Create a Sentry project for the app if needed (we want this for most apps):
+   - Send initial exceptions to Sentry project for dev, stage, and prod environments to create them.
+   - Create an alert for the prod environment only, with notifications sent to the appropriate team(s).
+   - If *not* using Sentry, delete Sentry configuration from my_function.py and test_my_function_.py, and remove sentry_sdk from project dependencies.
 
 # my_function
 
@@ -29,6 +33,7 @@ Description of the function/functions.
 
 ## Required ENV
 
+- `SENTRY_DSN` = If set to a valid Sentry DSN, enables Sentry exception monitoring. This is not needed for local development.
 - `WORKSPACE` = Set to `dev` for local development, this will be set to `stage` and `prod` in those environments by Terraform.
 
 ## Running locally
@@ -44,7 +49,7 @@ Description of the function/functions.
 - Run the default handler for the container:
 
   ```bash
-  docker run -p 9000:8080 my_function:latest
+  docker run -e WORKSPACE=dev -p 9000:8080 my_function:latest
   ```
 
 - Post to the container:

lambdas/my_function.py

@@ -1,10 +1,32 @@
 import json
 import logging
+import os
+
+import sentry_sdk
+from sentry_sdk.integrations.aws_lambda import AwsLambdaIntegration
 
 logger = logging.getLogger(__name__)
 logger.setLevel(logging.DEBUG)
 
+env = os.getenv("WORKSPACE")
+if sentry_dsn := os.getenv("SENTRY_DSN"):
+    sentry = sentry_sdk.init(
+        dsn=sentry_dsn,
+        environment=env,
+        integrations=[
+            AwsLambdaIntegration(),
+        ],
+        traces_sample_rate=1.0,
+    )
+    logger.info("Sentry DSN found, exceptions will be sent to Sentry with env=%s", env)
+else:
+    logger.info("No Sentry DSN found, exceptions will not be sent to Sentry")
+
 
 def lambda_handler(event: dict, context: object) -> str:  # noqa
+    if not os.getenv("WORKSPACE"):
+        raise RuntimeError("Required env variable WORKSPACE is not set")
+
     logger.debug(json.dumps(event))
+
     return "You have successfully called this lambda!"

tests/test_function.py

@@ -0,0 +1,34 @@
+from importlib import reload
+
+import pytest
+
+from lambdas import my_function
+
+
+def test_my_function_configures_sentry_if_dsn_present(caplog, monkeypatch):
+    monkeypatch.setenv("SENTRY_DSN", "https://1234567890@00000.ingest.sentry.io/123456")
+    reload(my_function)
+    assert (
+        "Sentry DSN found, exceptions will be sent to Sentry with env=test"
+        in caplog.text
+    )
+
+
+def test_my_function_doesnt_configure_sentry_if_dsn_not_present(caplog, monkeypatch):
+    monkeypatch.delenv("SENTRY_DSN", raising=False)
+    reload(my_function)
+    assert "No Sentry DSN found, exceptions will not be sent to Sentry" in caplog.text
+
+
+def test_lambda_handler_missing_workspace_env_raises_error(monkeypatch):
+    monkeypatch.delenv("WORKSPACE", raising=False)
+    with pytest.raises(RuntimeError) as error:
+        my_function.lambda_handler({}, {})
+    assert "Required env variable WORKSPACE is not set" in str(error)
+
+
+def test_my_function():
+    assert (
+        my_function.lambda_handler({}, {})
+        == "You have successfully called this lambda!"
+    )