Erlang Otp Applications

Read references/structure.md when deciding how to break a service into supervisors, workers, registries, or helper modules.

Failure Model

Assume unexpected errors should crash the current process. Do not bury faults behind catch-all error handling unless the failure is expected and part of the module contract.

Use supervisors to recover:

• Choose one_for_one when children are largely independent.
• Choose rest_for_one when later children depend on earlier ones.
• Choose one_for_all only when the whole sibling group must restart together.
• Use permanent, transient, and temporary child restart modes to express process intent.

Read references/failure-model.md when deciding how processes should fail, restart, shut down, or escalate errors.

Worker Selection Rules

Prefer:

• gen_server for stateful request/response services, resource ownership, and serialized access to mutable process state.
• supervisor for restart policy and child lifecycle management.
• Plain modules for pure logic.
• Short-lived spawned processes only when they have a clear lifecycle and supervision story.

Avoid:

• One large gen_server that owns unrelated responsibilities.
• Supervisors containing business logic.
• Swallowing exceptions and returning {error, Reason} for programmer bugs.
• Using process state as a substitute for clean module boundaries.

New Service Bootstrap

Use the starter template in assets/rebar3-otp-template for new services. It provides:

• rebar.config
• .app.src
• application callback module
• root supervisor
• sample gen_server worker

To materialize a copy with your application name, run:

python3 scripts/scaffold_rebar3_otp_app.py my_app /tmp/my_app

The script copies the template and rewrites myapp placeholders in file names and file contents.

Output Expectations

When using this skill for implementation or review:

• Show the proposed supervision tree.
• Name each process and its single responsibility.
• State the chosen restart strategy and why.
• State what should crash versus what should return tagged errors.
• Keep OTP callbacks thin and move domain logic into plain modules.