Add engineering handbook

Conventions covering naming, git workflow, commit messages, pull
requests, code review, GitHub standards, AWS infrastructure, SAM
project layout, and secrets management. Commit messages section
adapted from RomuloOliveira/commit-messages-guide (CC-BY-4.0).
This commit is contained in:
Adam Moussa 2026-05-02 16:42:44 -04:00
commit 0333e7f8f5
12 changed files with 945 additions and 0 deletions

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# Contributing
## How to Suggest Changes
- Open an issue describing the proposed change and why it's needed
- Or submit a PR with edits to the relevant markdown file
## Style Guidelines
- Keep it concise and scannable
- Use headers, bullet points, and code blocks
- One topic per file
- Concrete examples are better than abstract rules
- No emoji
## Adding a New Topic
If a convention doesn't fit into an existing file:
1. Create a new kebab-case markdown file at the root (e.g., `testing-standards.md`)
2. Add a link to it in `README.md` under the Contents section
3. Submit as a PR
## License
Contributions to this repository are licensed under [CC-BY-4.0](https://creativecommons.org/licenses/by/4.0/).

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# Engineering Handbook
Engineering conventions and best practices for Sea Haven Industries.
## Contents
- [Naming Conventions](naming-conventions.md) -- kebab-case everywhere, no exceptions
- [Git Workflow](git-workflow.md) -- feature branches, incremental commits, deploy-then-merge
- [Commit Messages](commit-messages.md) -- imperative mood, 50/72 rule, explain "why"
- [Pull Requests](pull-requests.md) -- scope, title, description format, merge strategy
- [Code Review](code-review.md) -- what to look for, giving feedback, turnaround expectations
- [GitHub Standards](github-standards.md) -- branch defaults, repo hygiene, Dependabot
- [AWS Infrastructure](aws-infrastructure.md) -- SAM vs CDK, Lambda defaults, CloudFormation
- [SAM Project Layout](sam-project-layout.md) -- standard directory structure for serverless projects
- [Secrets and Configuration](secrets-and-config.md) -- Secrets Manager vs SSM Parameter Store
## Contributing
See [CONTRIBUTING.md](CONTRIBUTING.md).
## License
This work is licensed under [CC-BY-4.0](https://creativecommons.org/licenses/by/4.0/). The commit messages section adapts content from [commit-messages-guide](https://github.com/RomuloOliveira/commit-messages-guide) by Romulo Oliveira, also licensed under CC-BY-4.0.

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# AWS Infrastructure
## IaC Strategy
- **SAM** is the default for new serverless stacks (Lambda + API Gateway + DynamoDB)
- **CDK** only for complex infrastructure (ECS, VPCs, multi-service compositions)
- Every deployed resource should be managed by CloudFormation
- No manually-created Lambdas, roles, or other resources outside of IaC
## Lambda Defaults
These apply to every Lambda in every project. Verify, don't assume.
| Setting | Value |
|---|---|
| Runtime | Python 3.12 or Node 22.x |
| Architecture | arm64 |
| Log retention | 60 days (explicit in IaC template) |
| Naming | kebab-case, matching the stack name prefix |
Never rely on the CloudWatch default for log retention. Always set `RetentionInDays` explicitly in the template.
## CloudFormation Outputs
Every stack should export:
- Function ARNs
- Any externally-consumable URLs (API Gateway endpoints, etc.)
## S3
- Every non-CloudFormation bucket must have `Purpose` and `ManagedBy` tags
- Define lifecycle policies in the IaC template
- Use Glacier Deep Archive for archival data
## README
Every repo must have a README that accurately describes:
- Project architecture
- Lambdas and services
- Data flow
- Configuration requirements
Update the README in the same commit where functionality changes. If a README is missing or outdated when you start working on a project, fix it as part of the current work.

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# Code Review
## Purpose
Code review exists to catch defects, share knowledge, and maintain consistency. It is not a gatekeeping exercise.
## What Reviewers Should Look For
### Always check
- Does the change do what the PR description says it does?
- Are there obvious bugs, edge cases, or error handling gaps?
- Does it follow [naming conventions](naming-conventions.md)?
- Are secrets handled correctly per [secrets-and-config.md](secrets-and-config.md)?
- If AWS resources changed, are Lambda defaults correct per [aws-infrastructure.md](aws-infrastructure.md)?
### Watch for
- Unused code, dead imports, or leftover debug statements
- Missing or outdated README updates for functionality changes
- Hardcoded values that should be in config or Secrets Manager
- Security concerns (input validation, injection, overly broad IAM policies)
### Don't nitpick
- Minor formatting differences handled by linters
- Personal style preferences that don't affect correctness
- Naming choices that are reasonable even if you'd pick something different
## Giving Feedback
- Be specific. "This might fail if the list is empty" is useful. "Needs work" is not.
- Distinguish between must-fix and suggestions. Prefix optional feedback with "nit:" or "suggestion:"
- Ask questions instead of making assumptions. "Is this intentional?" is better than "This is wrong."
- If a PR is good, say so. A simple "Looks good" is fine.
## Turnaround
- Aim to review within one business day of being requested
- If you can't review in time, say so and suggest another reviewer
- Don't let PRs sit in review for days without feedback
## Approving
- Approve when you're confident the change is correct and complete
- If you left suggestions but the PR is otherwise good, approve with comments rather than blocking
- One approval is sufficient for most changes

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# Commit Messages
> Adapted from [commit-messages-guide](https://github.com/RomuloOliveira/commit-messages-guide) by Romulo Oliveira, licensed under [CC-BY-4.0](https://creativecommons.org/licenses/by/4.0/).
## Rules
### Use imperative mood
Write what the commit *does*, not what you *did*.
| Good | Bad |
|---|---|
| Add retry logic to payment processor | Added retry logic to payment processor |
| Fix null check in auth handler | Fixed null check in auth handler |
| Remove deprecated endpoint | Removing deprecated endpoint |
### Capitalize the first letter
| Good | Bad |
|---|---|
| Fix null check in auth handler | fix null check in auth handler |
### Keep the subject line under 50 characters
The subject line is for scanning. Details go in the body.
### Wrap the body at 72 characters
If you need to explain more, add a blank line after the subject and write a body wrapped at 72 characters per line.
### Explain "why," not "what"
The diff shows what changed. The commit message should explain why.
| Good | Bad |
|---|---|
| Increase timeout to handle slow upstream responses | Change timeout from 30 to 60 |
| Switch to arm64 to reduce Lambda cold start cost | Update architecture setting |
### No generic messages
These are not acceptable:
- `Fix stuff`
- `Update code`
- `WIP`
- `Misc changes`
- `Address review comments`
Every commit should describe a specific change.
### No self-referential language
| Good | Bad |
|---|---|
| Fix race condition in queue processor | This commit fixes a race condition |
| Add input validation for email field | This PR adds validation |
| Refactor auth middleware for clarity | I refactored the auth middleware |
## Template
```
Subject line (50 chars max, imperative, capitalized)
Optional body wrapped at 72 characters. Explain the problem
this commit solves and why this approach was chosen. Mention
side effects or non-obvious consequences.
Refs: #123
```
## Example
```
Add retry logic for transient upstream failures
The payment processor occasionally returns 503 during
deployments. Without retries, these surface as user-facing
errors. This adds exponential backoff with 3 attempts,
which matches the upstream's documented recovery window.
Refs: #45
```

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# Git Workflow
## Branching
- Never commit directly to `main`
- Delete branches after merge
- Use the appropriate branch prefix for the type of work:
| Prefix | Use when |
|---|---|
| `feature/<description>` | Adding new functionality or enhancing existing features |
| `bug/<description>` | Fixing a non-urgent defect found during development or testing |
| `hotfix/<description>` | Fixing a production issue that needs immediate attention |
**bug vs hotfix:** Use `bug/` for defects caught before they affect production (failing tests, broken dev flows, issues found in review). Use `hotfix/` only when production is impacted and the fix needs to bypass normal review cadence.
## Commits
- Commit each logical change individually with a descriptive message
- See [commit-messages.md](commit-messages.md) for formatting rules
- Keep the working tree clean: commit or stash before switching context
## Deploy-Then-Merge
The standard flow for changes that deploy to AWS:
1. Create a feature branch (`feature/add-receipt-parser`)
2. Develop and commit locally
3. Open a PR via `gh pr create`
4. Merge the feature branch into `main` locally
5. Deploy to the target environment (`sam deploy`, etc.)
6. Verify in production
7. Merge the PR on GitHub
This ensures production works before the PR closes. If the deploy fails, the PR stays open and `main` on GitHub is still clean.
## Push Discipline
- Push regularly; don't accumulate unpushed commits
- Never force push `main`
- Never amend or rewrite commits already pushed to `main`
- If you need to add context to a past change, use PR descriptions or issue comments
## Versioning
Use [Semantic Versioning](https://semver.org/) (SemVer) as the standard: `MAJOR.MINOR.PATCH`.
| Increment | When |
|---|---|
| `MAJOR` | Breaking changes to the public API or contract (removed endpoints, changed request/response shapes, incompatible config changes) |
| `MINOR` | New functionality that is backwards-compatible (new endpoints, new optional fields, new features) |
| `PATCH` | Backwards-compatible bug fixes, dependency updates, documentation corrections |
### When to version
Not every project needs versioning. Apply SemVer when the project has consumers that depend on its interface:
| Version | Don't version |
|---|---|
| Published packages (npm, PyPI) | Internal SAM stacks with no external consumers |
| Public APIs with external consumers | One-off scripts and migration tools |
| Shared libraries used across repos | Internal tools used only by the team that builds them |
| CLIs distributed to users | |
### How to tag
Create annotated tags on `main` after the PR is merged:
```bash
git tag -a v1.2.0 -m "v1.2.0"
git push origin v1.2.0
```
Start at `v0.1.0` for new projects. Move to `v1.0.0` when the interface is stable and has external consumers.
## Cleaning Up
After a PR is merged:
```bash
git checkout main
git pull
git branch -d feature/add-receipt-parser
```
Don't let stale local branches or untracked project directories accumulate.

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# GitHub Standards
## Repository Defaults
- Default branch: `main`
- Every repo gets a one-line description
- Default to `private` visibility for org repos
- Dependabot alerts and security updates enabled on all active repos
## Branch Protection
- Require a PR for merges to `main` (no direct push)
- No force push to `main`
- No branch deletion for `main`
## Repo Hygiene
- Delete feature branches after merge
- Archive repos that are no longer actively developed (close issues first)
- Don't delete repos unless truly disposable
- Scrub all company-specific info from git history before making any repo public
## Public Repos
Before making a repo public, verify the entire git history contains no:
- Phone numbers or customer data
- API subdomains or internal URLs
- Webhook endpoints
- Employee names or internal identifiers
If sensitive data was committed at any point, start fresh with a clean `git init` rather than rewriting history.

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# Naming Conventions
## The Rule
kebab-case for everything. No exceptions.
No `snake_case`, `PascalCase`, or mixed styles anywhere.
## Where It Applies
| Resource | Example |
|---|---|
| Repository names | `expense-approval-bot`, `door-unlock-api` |
| CloudFormation stack names | `expense-approval-bot` (must match repo name) |
| Lambda function names | `expense-approval-bot-process-receipt` |
| DynamoDB table names | `expense-approval-bot-receipts` |
| S3 bucket names | `expense-approval-bot-uploads` |
| Secrets Manager secrets | `expense-approval-bot/slack-signing` |
| Feature branches | `feature/add-receipt-parser` |
## CDK Gotcha
CDK generates PascalCase stack names by default. Always set an explicit `stackName` (TypeScript) or `stack_name` (Python) in your stack definition to enforce kebab-case.
```typescript
new MyStack(app, 'MyStack', {
stackName: 'my-stack',
});
```
## Examples
| Bad | Good | Why |
|---|---|---|
| `ExpenseApprovalBot` | `expense-approval-bot` | PascalCase |
| `expense_approval_bot` | `expense-approval-bot` | snake_case |
| `expenseApprovalBot` | `expense-approval-bot` | camelCase |
| `Expense-Approval-Bot` | `expense-approval-bot` | Mixed case |
| `feature/AddParser` | `feature/add-parser` | PascalCase in branch |

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# Pull Requests
## Scope
Each PR should represent a single logical change. If you find yourself writing "and" in the title, consider splitting it into separate PRs.
| Good scope | Too broad |
|---|---|
| Add receipt parser Lambda | Add receipt parser and refactor auth middleware |
| Fix timeout in payment processor | Fix timeout and update dependencies |
| Update Lambda runtime to Python 3.12 | Update runtime and add new endpoint |
## Title
- Keep it under 70 characters
- Use imperative mood, same as commit messages
- Describe the change, not the ticket
| Good | Bad |
|---|---|
| Add retry logic for transient upstream failures | JIRA-123 |
| Fix null check in auth handler | Bug fix |
| Update Lambda runtime to Python 3.12 | Updates |
## Description
Use a structured format:
```markdown
## Summary
Brief explanation of what this PR does and why.
## Changes
- Bullet list of specific changes
## Test Plan
- How you verified this works
- What to check during review
```
The summary should explain **why** the change is needed, not just restate the diff. Reviewers can read the code; they need context.
## When to Open a PR
- Before deploying to production (see [deploy-then-merge](git-workflow.md) workflow)
- When the work is ready for review, not as a draft for parking incomplete work
- After verifying locally that the change works as expected
## Merging
- Squash merge for feature branches with messy interim commits
- Regular merge for branches with clean, meaningful commit history
- Delete the branch after merge

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# SAM Project Layout
## Standard Directory Structure
```
project-name/
├── template.yaml # SAM template at root
├── samconfig.toml # Deploy config (gitignored)
├── samconfig.toml.example # Template for onboarding (committed)
├── src/
│ ├── function_name/
│ │ ├── app.py # Lambda handler
│ │ └── requirements.txt # Per-function dependencies
│ └── shared/ # Shared layer code (if needed)
└── .gitignore
```
## File Purposes
### `template.yaml`
The SAM/CloudFormation template. Lives at the project root. Defines all Lambda functions, IAM roles, API Gateway endpoints, DynamoDB tables, and other resources.
### `samconfig.toml`
Contains real ARNs, S3 bucket names, and deploy parameters. **Gitignored** because it varies per environment and may contain account-specific values.
### `samconfig.toml.example`
A committed template showing the expected structure and parameter names. New contributors copy this to `samconfig.toml` and fill in their values.
### `src/function_name/`
One directory per Lambda function. Each contains its own handler (`app.py`) and dependencies (`requirements.txt`). This keeps functions independently deployable and avoids bloating one function with another's dependencies.
### `src/shared/`
Optional. Used for code shared across multiple functions, typically deployed as a Lambda layer.
## Standard .gitignore
```
.aws-sam/
__pycache__/
*.pyc
.env
samconfig.toml
```

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# Secrets and Configuration
## The Boundary
There is a strict separation between sensitive and non-sensitive configuration. No gray areas.
## AWS Secrets Manager
Use Secrets Manager for **all** sensitive values:
- API access tokens and keys
- Signing values used for request verification
- Webhook URLs that act as implicit authentication
- Database connection strings with embedded passwords
- Any value that would be dangerous if leaked
When in doubt about whether something qualifies as sensitive, treat it as sensitive.
### Naming Convention
```
stack-name/value-name
```
Examples:
- `my-stack/slack-signing`
- `my-stack/stripe-key`
## SSM Parameter Store
Use Parameter Store **only** for non-sensitive configuration:
- Feature flags
- Endpoint URLs (public, non-authenticated)
- Schedule expressions
- Channel IDs and non-sensitive identifiers
## Lambda Pattern
1. Store the sensitive value in Secrets Manager
2. Grant the function's IAM role `secretsmanager:GetSecretValue` scoped to only the values it needs
3. Read the value on cold start via the AWS SDK
4. Cache it in a module-level variable so subsequent invocations reuse it
```python
import boto3
import json
_client = boto3.client('secretsmanager')
_cached = None
def get_config():
global _cached
if _cached is None:
resp = _client.get_secret_value(SecretId='my-stack/config')
_cached = json.loads(resp['SecretString'])
return _cached
def handler(event, context):
config = get_config()
# use config values
```
## What NOT to Do
- **Never use Lambda environment variables for sensitive values.** Even with `NoEcho` CloudFormation parameters, the values end up as plaintext in the Lambda console and are readable by anyone with `GetFunctionConfiguration` access.
- **Never commit `.env` files** containing real values to a repository.
- **Never store sensitive values** in Notion, Slack messages, or other plaintext documents.