Lab: find out why your variable never took effect

Environment variables resolve through three tiers, and the lesson stated the order. This is what it feels like from the inside when you set a value and it does not appear.

1. 1

   Model the three tiers and resolve.

   bash Copy

   cat > /tmp/prec.py <<'EOF'
   shared = {"DATABASE_URL": "postgres://shared/app", "LOG_LEVEL": "info"}
   vault  = {"DATABASE_URL": "postgres://vault/app"}
   branch = {"DATABASE_URL": "postgres://branch/app"}
   
   def resolve(git_branch=None):
       out = dict(shared)          # shared
       out.update(vault)           # vault beats shared
       if git_branch:
           out.update(branch)      # branch override beats both
       return out
   
   print("you set DATABASE_URL at the org level to:", shared["DATABASE_URL"])
   print("preview resolves to:                     ", resolve()["DATABASE_URL"])
   print("preview on feat/x resolves to:           ", resolve("feat/x")["DATABASE_URL"])
   print("\nLOG_LEVEL, which only exists at the org level:", resolve()["LOG_LEVEL"])
   EOF
   python3 /tmp/prec.py

2. 2

   Your org-level value is present, correct, and irrelevant for this key.

   text Copy

   you set DATABASE_URL at the org level to: postgres://shared/app
   preview resolves to:                      postgres://vault/app
   preview on feat/x resolves to:            postgres://branch/app
   
   LOG_LEVEL, which only exists at the org level: info

3. 3

   Clean up.

   bash Copy

   rm /tmp/prec.py

Shadowing is silent by design. Nothing errors, nothing warns, and the value you set is stored exactly as you wrote it. LOG_LEVEL proves the org tier works fine; DATABASE_URL simply has a more specific value that wins.

• The precedence is shared, then vault, then branch override, and more specific always wins.
• A branch override left behind by a deleted feature branch is the version of this that is hardest to find, because nothing in the current codebase mentions it.
• The resolve endpoint returns the final set with precedence already applied. Reading it is faster than reasoning about which tier you forgot.