RFC370: CLI Deploy Approval With Change Set Review

Author: orien

text/0370-cli-deploy-changeset-review.md

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+# Enhanced CLI Deploy Approval With Change Set Review
+
+* **Original Author(s):**: @stevehodgkiss, @orien
+* **Tracking Issue**: #370
+* **API Bar Raiser**: @{BAR_RAISER_USER}
+
+This feature enhances the existing `--require-approval=any-change` option to show all stack changes (not just
+security changes) and integrates CloudFormation change set creation and review to provide users with an accurate
+preview of what will be applied before deployment execution.
+
+Modern cloud infrastructure contains critical stateful resources—databases, persistent storage, message queues, and
+other systems that hold valuable data and maintain complex state. Engineers deploying changes to these environments
+carry significant responsibility: a single misunderstood deployment can lead to data loss, service outages, or
+security vulnerabilities that affect customers and business operations. While Infrastructure as Code provides
+repeatability and version control, it doesn't eliminate the fundamental need for engineers to understand precisely
+what changes will be applied before execution. Tooling must bridge this gap by providing clear, accurate previews
+of deployment impact—especially for stateful resources where "undo" isn't always possible. This enhancement ensures
+that engineers have the complete information they need to make informed decisions about infrastructure changes.
+
+## Working Backwards
+
+### CHANGELOG
+
+* **feat(cli)**: enhance `--require-approval=any-change` to show all stack changes instead of only security changes
+* **feat(cli)**: integrate CloudFormation change set creation and display when using `--require-approval=any-change`
+  with standard (non-hotswap) deployments
+
+The `cdk deploy --require-approval=any-change` command now shows all changes to the stack, not just security-related
+changes. For standard CloudFormation deployments, it creates a CloudFormation change set, displays both the template
+diff and the change set details, and prompts for approval before executing the change set. This provides users with
+the most accurate preview of what changes will actually be applied.
+
+```bash
+# Review all changes before deploying (enhanced behavior)
+cdk deploy --require-approval=any-change MyStack
+
+# Existing security-only behavior unchanged
+cdk deploy --require-approval=broadening MyStack
+
+# No change set review with hotswap (template diff only)
+cdk deploy --require-approval=any-change --hotswap MyStack
+```
+
+### README
+
+#### Enhanced Change Approval
+
+The `--require-approval=any-change` option has been enhanced to provide comprehensive change review:
+
+##### Standard Deployments (without --hotswap)
+
+When using standard CloudFormation deployments, `--require-approval=any-change` now:
+
+1. **Shows All Changes**: Displays template diffs for all resource changes, not just security changes
+2. **Creates Change Set**: Automatically creates a CloudFormation change set for accurate deployment preview
+3. **Combined Display**: Shows both template diff and change set information
+4. **Accurate Resource Impact**: Displays physical resource changes, replacements, and dependencies
+5. **Requires Approval**: Prompts for confirmation before executing the change set
+
+##### Example Output
+
+```
+$ cdk deploy --require-approval=any-change MyWebApp
+
+Template Changes:
+ [+] AWS::S3::Bucket WebAppBucket
+ [~] AWS::Lambda::Function WebAppFunction
+     └─ Runtime: nodejs14.x → nodejs18.x
+     └─ MemorySize: 128 → 256
+ [~] AWS::IAM::Role WebAppRole
+
+Creating change set for detailed deployment preview...
+Change set created: cdk-deploy-change-set-2023-12-01-143022
+
+CloudFormation Change Set Details:
+┌──────────────────────┬──────────┬─────────────────────────┬─────────────────┬─────────────────┐
+│ Resource Type        │ Action   │ Logical ID              │ Physical ID     │ Replacement     │
+├──────────────────────┼──────────┼─────────────────────────┼─────────────────┼─────────────────┤
+│ AWS::S3::Bucket      │ Add      │ WebAppBucket            │ -               │ -               │
+│ AWS::Lambda::Function│ Modify   │ WebAppFunction          │ MyWebApp-Fn123  │ False           │
+│ AWS::IAM::Role       │ Modify   │ WebAppRole              │ MyWebApp-Role   │ False           │
+└──────────────────────┴──────────┴─────────────────────────┴─────────────────┴─────────────────┘
+
+🔒 Security Changes:
+   • WebAppRole: Adding permissions for s3:PutObject, s3:GetObject
+
+📝 Parameter Changes (not visible in template):
+   • LambdaVersion parameter updated (triggers function update)
+
+Do you approve these changes? [y/N]: y
+
+Executing change set...
+✅ Stack MyWebApp deployed successfully
+```
+
+##### Hotswap Deployments
+
+When using `--require-approval=any-change` with `--hotswap`, the behavior is enhanced:
+
+- Shows template diff for all changes (previously only showed security changes)
+- No change set creation (hotswap bypasses CloudFormation)
+- Proceeds with hotswap deployment after approval
+
+##### Existing Options Unchanged
+
+- `--require-approval=never`: No approval required (default)
+- `--require-approval=broadening`: Only security-broadening changes require approval (unchanged behavior)
+
+---
+
+Ticking the box below indicates that the public API of this RFC has been
+signed-off by the API bar raiser (the `status/api-approved` label was applied to the
+RFC pull request):
+
+```
+[ ] Signed-off by API Bar Raiser @xxxxx
+```
+
+## Public FAQ
+
+### What are we launching today?
+
+We are launching enhanced functionality for the existing `--require-approval=any-change` flag. This enhancement makes
+the flag show all stack changes (not just security changes) and integrates CloudFormation change set creation for
+standard deployments. Users get both template diff information and accurate change set details, showing exactly what
+CloudFormation will execute.
+
+### Why should I use this feature?
+
+The enhanced `--require-approval=any-change` addresses several use cases:
+
+1. **Complete Change Visibility**: See all changes to your stack, not just security changes
+2. **Accurate Deployment Preview**: Change sets show the actual changes CloudFormation will make, including parameter
+   updates that don't appear in template diffs
+3. **Resource Replacement Detection**: Change sets indicate when resources will be replaced, preventing data loss
+4. **Production Safety**: Required approval step prevents accidental, destructive deployments
+5. **Compliance**: Manual review process for infrastructure changes
+6. **Parameter-Only Deployments**: Visibility into CloudFormation parameter changes that trigger resource updates
+
+This is particularly valuable for production environments and teams with change management requirements.
+
+## Internal FAQ
+
+### Why are we doing this?
+
+The current `--require-approval=any-change` option is misleading - it only shows security-related changes, not all
+changes as the name implies. This affects both standard and hotswap deployments. Users who want to review all changes
+before deployment don't have a good option. Additionally, template diffs don't show the complete picture of what
+CloudFormation will actually do:
+
+1. **Parameter Changes**: CloudFormation parameter updates that trigger resource changes don't show in template diffs
+2. **Resource Replacement**: Template diffs don't indicate when resources will be replaced vs. updated in-place
+3. **Dependency Changes**: Order of operations and dependencies are not visible in template diffs
+4. **Physical Resource Impact**: Template diffs show logical changes but not physical resource impacts
+
+CloudFormation change sets provide definitive information about what will actually happen during deployment. The
+[original implementation attempt](https://github.com/aws/aws-cdk/pull/15494) demonstrated the value of this approach.
+
+### Why should we _not_ do this?
+
+This change modifies existing behavior, which could be disruptive:
+
+1. **Behavior Change**: `--require-approval=any-change` currently only shows security changes; expanding to all changes
+   could be unexpected
+2. **Performance Impact**: Creating change sets adds latency to the deployment process
+3. **Hotswap Incompatibility**: Change sets cannot work with hotswap deployments, creating an inconsistent user experience
+4. **API Dependencies**: Additional CloudFormation API calls and potential rate limiting
+5. **Complexity**: More code paths to maintain and test
+
+However, these concerns are mitigated by the fact that the current behavior is already misleading (the name suggests
+all changes, but only shows security changes), and the performance impact only affects users who explicitly opt into
+the approval process.
+
+### What is the technical solution (design) of this feature?
+
+The implementation enhances the existing `--require-approval` logic with change set integration:
+
+#### High-Level Flow
+
+1. **Synthesis**: Standard CDK app synthesis to generate CloudFormation templates
+2. **Approval Check**: Determine if approval is required based on `--require-approval` value
+3. **Template Diff**: Generate template diff showing all changes (enhanced from current security-only logic)
+4. **Deployment Type Check**:
+   - For hotswap deployments: show template diff and proceed with existing approval flow
+   - For standard deployments: continue to change set creation
+5. **Change Set Creation**: Call CloudFormation `CreateChangeSet` API
+6. **Combined Display**: Show both template diff and change set information
+7. **User Approval**: Interactive prompt for confirmation
+8. **Change Set Execution**: Call `ExecuteChangeSet` API on approval
+
+#### Key Components
+
+1. **Enhanced DiffAnalyzer**: Modify existing logic to detect all changes instead of only security changes
+2. **ChangeSetCreator**: New component to create and describe CloudFormation change sets
+3. **CombinedDisplayFormatter**: Format both template diff and change set information
+4. **ApprovalPrompt**: Enhanced to handle both template diff and change set approval
+
+#### Change Set Integration
+
+- **Automatic Creation**: Change sets are created automatically for `--require-approval=any-change` on standard
+  deployments
+- **Naming Convention**: `cdk-deploy-change-set-{timestamp}` to avoid conflicts
+- **Cleanup**: Change sets are automatically deleted after successful execution or on cancellation
+- **Error Handling**: Graceful fallback to template diff only if change set creation fails
+
+### Is this a breaking change?
+
+This is technically a breaking change in behavior, but it aligns with user expectations:
+
+**Breaking aspects**:
+
+- `--require-approval=any-change` will now show all changes instead of only security changes (affects both standard and hotswap deployments)
+- Additional latency due to change set creation for standard deployments
+- Different approval prompts that include change set information for standard deployments
+- Hotswap deployments will show template diffs for all changes instead of only security changes
+
+**Mitigation**:
+
+- The current behavior is misleading - users expect "any-change" to mean all changes
+- Users explicitly opt into this behavior with the flag
+- Existing `--require-approval=broadening` behavior remains unchanged
+- Performance impact only affects users who choose to use approval
+
+**Migration path**:
+
+- Users who want the old security-only behavior should use `--require-approval=broadening`
+- Documentation will clearly explain the enhanced behavior
+
+### What alternative solutions did you consider?
+
+#### 1. Add New `--require-approval=all-changes` Option
+
+Add a new option value instead of changing existing behavior.
+**Rejected**: Would leave the misleading `any-change` option unchanged and create confusion between `any-change` and
+`all-changes`.
+
+#### 2. Create Separate `--review-changeset` Flag
+
+Add a separate flag specifically for change set review.
+**Rejected**: Creates fragmented functionality; approval and change set review are closely related concerns that should
+be unified.
+
+#### 3. Always Create Change Sets for Any Approval
+
+Create change sets for all `--require-approval` modes.
+**Rejected**: Unnecessary overhead for security-only approval workflows.
+
+#### 4. Only Show Change Sets, Remove Template Diff
+
+Show only change set information without template diff.
+**Rejected**: Template diffs provide valuable context about CDK-level changes that complement change set physical
+resource information.
+
+### What are the drawbacks of this solution?
+
+1. **Behavioral Breaking Change**: Existing `--require-approval=any-change` users will see different behavior
+2. **Performance Impact**: Change set creation adds 5-15 seconds to the deployment process
+3. **Inconsistent Experience**: Different behavior between hotswap and standard deployments
+4. **Additional API Calls**: More CloudFormation API usage and potential throttling
+5. **Complexity**: More code paths and error handling scenarios
+6. **User Confusion**: Users may not understand why some deployments show change sets and others don't
+
+### What is the high-level project plan?
+
+#### Phase 1: Core Implementation
+
+- Modify existing `--require-approval=any-change` logic to show all changes instead of security-only
+- Implement change set creation for standard (non-hotswap) deployments
+- Add combined display of template diff and change set information
+- Update approval prompt to handle change set confirmation
+
+#### Phase 2: Polish & Integration
+
+- Implement change set cleanup on success/failure
+- Add comprehensive error handling for change set creation failures
+- Optimize display formatting for large change sets
+- Add a configuration option in `cdk.json` for change set timeout
+
+#### Phase 3: Documentation & Migration
+
+- Update CLI help text and documentation
+- Create a migration guide for users affected by the behavior change
+- Add examples and best practices
+- Performance optimization based on usage patterns
+
+### Are there any open issues that need to be addressed later?
+
+1. **User Communication**: How to best communicate the behavior change to existing users
+2. **Change Set Cleanup**: Automatic cleanup strategy for failed or cancelled deployments
+3. **Large Change Sets**: Optimal display format for deployments with hundreds of resources
+4. **Nested Stacks**: Change set behavior with nested stack deployments
+5. **Performance Optimization**: Caching strategies to reduce change set creation time
+6. **Error Recovery**: Fallback strategies when change set creation fails
+7. **Configuration**: Options to disable change set creation for specific environments
+
+## Appendix
+
+### CloudFormation Change Set API Reference
+
+- [`CreateChangeSet`](https://docs.aws.amazon.com/AWSCloudFormation/latest/APIReference/API_CreateChangeSet.html):
+  Create change set for deployment preview
+- [`DescribeChangeSet`](https://docs.aws.amazon.com/AWSCloudFormation/latest/APIReference/API_DescribeChangeSet.html):
+  Get detailed change set information
+- [`ExecuteChangeSet`](https://docs.aws.amazon.com/AWSCloudFormation/latest/APIReference/API_ExecuteChangeSet.html):
+  Execute approved changes
+- [`DeleteChangeSet`](https://docs.aws.amazon.com/AWSCloudFormation/latest/APIReference/API_DeleteChangeSet.html):
+  Clean up change sets after execution or cancellation
+
+### Current vs Enhanced Behavior
+
+| Scenario | Current Behavior | Enhanced Behavior |
+|----------|------------------|-------------------|
+| `--require-approval=any-change` (standard deploy) | Shows only security changes, direct deploy | Shows all changes + change set, execute change set |
+| `--require-approval=any-change` (hotswap) | Shows only security changes, hotswap deploy | Shows all changes, hotswap deploy |
+| `--require-approval=broadening` | Shows security changes, direct deploy | **Unchanged** |
+| `--require-approval=never` | No approval, direct deploy | **Unchanged** |
+
+### Hotswap Compatibility
+
+Hotswap deployments bypass CloudFormation entirely, making them incompatible with change sets:
+
+- **With hotswap**: Template diff shows all changes, approval prompt, then hotswap deployment (no change set)
+- **Without hotswap**: Template diff + change set details, approval prompt, then change set execution
+
+### Migration Guide
+
+**For users currently using `--require-approval=any-change`:**
+
+**Before (current behavior):**
+
+- Only security-related changes shown in template diff
+- Direct CloudFormation deployment (standard) or hotswap deployment
+- Fast deployment after approval
+
+**After (enhanced behavior):**
+
+- All changes shown in template diff (security + non-security)
+- **Standard deployments**: Change set creation and review + template diff
+- **Hotswap deployments**: Enhanced template diff showing all changes (no change set)
+- Slightly slower for standard deployments due to change set creation
+- More accurate preview of deployment impact
+
+**If you want the old behavior:**
+Use `--require-approval=broadening` which maintains the current security-only focus.
+
+### Example Scenarios
+
+#### Scenario 1: Lambda Function Update
+
+```bash
+# Template shows: Lambda function code change
+# Change set shows: UpdateFunctionCode API call, no replacement
+# User sees: Both perspectives for complete understanding
+```
+
+#### Scenario 2: RDS Parameter Change
+
+```bash
+# Template shows: No visible changes (parameter-only update)
+# Change set shows: Database replacement required due to parameter change, ALL DATA WILL BE LOST
+# User sees: Critical information that template diff cannot provide
+```
+
+#### Scenario 3: Security Group Modification
+
+```bash
+# Template shows: Security group rule changes
+# Change set shows: Which EC2 instances will be affected by the change
+# User sees: Both logical and physical impact of the change
+```