Allow different configs for different machines

Introduces environment variables template file and tasks related to the
environment variables files. You're supposed to create a `.env.local`
and a `.env.prod` based on `.env.template`. There's a task that ensures
the keys in `.env.template` are also present in the other files. There's
another task that sets the environment variables in production.

For:
#12

.ebignore

@@ -1,3 +1,8 @@
+# Environment variables:
+.env.local
+.env.prod
+
+# Python stuff:
 .coverage
 .mypy_cache
 .pytest_cache

.env.template

@@ -0,0 +1 @@
+export SOME_VAR="Test"

.gitignore

@@ -1,7 +1,13 @@
+# Elastic Beanstalk stuff:
 !.elasticbeanstalk/*.cfg.yml
 !.elasticbeanstalk/*.global.yml
 .elasticbeanstalk/*
 
+# Environment variable files:
+.env.local
+.env.prod
+
+# Python stuff:
 .coverage
 .mypy_cache
 .pytest_cache

Pipfile

@@ -13,6 +13,7 @@ mypy = "*"
 pytest = "*"
 invoke = "*"
 coverage = "*"
+python-dotenv = "*"
 
 [requires]
 python_version = "3.12"

README.md

@@ -22,6 +22,12 @@ For all other command line tasks, the affils project uses [Invoke](https://docs.
 We have diagrams for our current and desired affiliations workflow in
 the [diagrams directory](./doc/diagrams).
 
+## Environment variables
+
+We use environment variables files (commonly referred to as `.env`
+files) to configure the affiliations service. For more info on how we
+use `.env` files, see the [doc on environment variables](./doc/envars.md).
+
 ## Deployment
 
 Read the [doc](./doc/deploy.md) on deploying to production.

doc/envars.md

@@ -0,0 +1,12 @@
+# Environment variables
+
+There's a `.env.template` file that is the source of truth for
+environment variable keys. You're supposed to create a `.env.local` file
+and a `.env.prod` file based on `.env.template`. The keys in each
+environment variable file should stay the same at all times. This is
+enforced programmatically using Invoke tasks. (See the `tasks.py` file
+for more details on this.) The values of the keys can differ between
+files, of course.
+
+When you deploy to production, the production environment variables are
+automatically uploaded to production.

requirements.txt

@@ -22,6 +22,7 @@ platformdirs==4.2.0
 pluggy==1.4.0
 pylint==3.1.0
 pytest==8.1.1
+python-dotenv==1.0.1
 tomlkit==0.12.4
 typing_extensions==4.10.0
 Werkzeug==3.0.1

src/app.py

@@ -4,6 +4,7 @@
 """
 
 # Built-in libraries:
+import os
 import subprocess
 
 # Third-party dependencies:
@@ -28,3 +29,9 @@ def current_git_sha():
     # Strip newline character from the end of the string.
     sha = output[0 : len(output) - 1]
     return sha
+
+
+@app.route("/env")
+def display_env_var():
+    """Displays environment variable for testing purposes."""
+    return os.environ.get("SOME_VAR")

tasks.py

@@ -5,8 +5,20 @@
 """
 
 # Third-party dependencies:
+from dotenv import dotenv_values
 from invoke import task
 
+# Environment variable files:
+ENV_TRUTH = ".env.template"  # The source of truth for all .env files.
+ENV_LOCAL = ".env.local"
+ENV_PROD = ".env.prod"
+
+# Configs:
+TRUTH_CONFIG = dotenv_values(ENV_TRUTH)
+LOCAL_CONFIG = dotenv_values(ENV_LOCAL)
+PROD_CONFIG = dotenv_values(ENV_PROD)
+CONFIGS = [LOCAL_CONFIG, PROD_CONFIG]
+
 
 @task
 def fmt(c):
@@ -32,18 +44,29 @@ def test(c):
     c.run("coverage run -m pytest && coverage report")
 
 
-@task(pre=[fmt, lint, types, test])
+@task
+def envsame(c):
+    """Ensure environment variable keys match in each .env file."""
+    for config in CONFIGS:
+        if config.keys() != TRUTH_CONFIG.keys():
+            print(".env keys do not match. Check your .env files.")
+            exit(1)
+
+
+@task(pre=[fmt, lint, types, test, envsame])
 def check(c):
     """Run all code checks."""
 
 
 @task
 def reqs(c):
-    """Generate requirements.txt file for use in GitHub Actions.
+    """Generate requirements.txt file.
 
     The GitHub Actions workflow runners don't seem to play nicely with
     Pipenv. We generate a requirements.txt file and use it to install
     dependencies in GitHub Actions.
+
+    We also use the requirements.txt file on Elastic Beanstalk.
     """
     add_warning = (
         "echo '# Do not edit directly. This file is generated.\n' > requirements.txt"
@@ -61,10 +84,19 @@ def dev(c):
 
     Assumes you've activated the virtual environment.
     """
-    c.run("cd src && flask run")
+    c.run(f"source {ENV_LOCAL} && cd src && flask run")
 
 
-@task
+@task(pre=[envsame])
+def envprod(c):
+    """Set production environment variables."""
+    vars = " ".join([f"{key}={val}" for key, val in PROD_CONFIG.items()])
+    c.run(f"eb setenv {vars}")
+
+
+# Make sure our requirements.txt is up-to-date before we deploy.
+# Set environment variables before we deploy.
+@task(pre=[reqs, envprod])
 def deploy(c):
     """Deploy the affils service.