Agenda Fetcher Lambda Implementation

[ramtoearth]

Agenda Fetcher Lambda Implementation

Objective: Create a serverless function that detects changes in Sessionize API and triggers downstream actions only when changes occur.

Functional Requirements

1. Input Handling:

   • Accept POST requests with JSON body containing api_url parameter
   • Validate presence of api_url
   • Return 400 error if missing

2. Data Fetching:

   • Fetch JSON data from provided api_url
   • Handle HTTP errors (non-2xx responses)

3. Change Detection:

   • Compute MD5 hash of fetched JSON payload
   • Store/retrieve last known hash in DynamoDB
   • Compare current hash with stored hash
   • Track three states:
     • First run (no existing hash)
     • Changed data
     • Unchanged data

4. State Management:

   • Store initial hash in DynamoDB on first run
   • Update hash when changes detected
   • Maintain updatedAt timestamp

5. Action Trigger:

   • Set mutation flag when:
     • First run (no existing hash)
     • Hash mismatch (changed data)
   • Skip mutation when hash unchanged

6. Response:

   • Return 200 with { changed: boolean }
   • Include metrics for each state

7. Error Handling:

   • Catch all processing errors
   • Return 500 for unexpected errors
   • Log detailed errors with context

Non-Functional Requirements

1. Observability:

   • Integrate AWS Powertools:
     • Logger for structured logging
     • Tracer for AWS call instrumentation
     • Metrics for state tracking
   • Add middleware for automatic context injection

2. Infrastructure:

   • Use DynamoDB table with single-item design
   • Configure environment variables:
     • DYNAMODB_TABLE_NAME
     • DYNAMODB_HASH_KEY

3. Efficiency:

   • Only trigger downstream actions when data changes
   • Avoid unnecessary network calls
   • Optimize DynamoDB operations

Flowchart Diagram

%%{init: {'theme': 'dark', 'themeVariables': { 'primaryColor': '#1e1e2e'}}}%%
flowchart TD
    A([Start]) --> B[Parse Event Body]
    B --> C{api_url present?}
    C -->|No| D[Return 400 Error]
    C -->|Yes| E[Fetch External API]
    E --> F{API Response OK?}
    F -->|No| G[Throw Error]
    F -->|Yes| H[Compute JSON Hash]
    H --> I[Get Last Hash from DynamoDB]
    I --> J{Item exists?}
    J -->|No| K[Store New Hash\nSet mutation flag=true]
    J -->|Yes| L{Hash Changed?}
    L -->|No| M[Set flag=false\nMetric: NoChange]
    L -->|Yes| N[Update Hash\nSet flag=true\nMetric: HashChanged]
    K --> O{Mutation needed?}
    N --> O
    M --> O
    O -->|flag=true| P[Execute Mutation\nMetric: MutationInvoked]
    O -->|flag=false| Q[Skip Mutation]
    P --> R[Return 200\nchanged: true]
    Q --> S[Return 200\nchanged: false]
    G --> T[Log Error]
    T --> U[Return 500 Error]
    D --> U
    
    style A fill:#2ecc71,stroke:#27ae60
    style U fill:#e74c3c,stroke:#c0392b
    style R fill:#3498db,stroke:#2980b9
    style S fill:#3498db,stroke:#2980b9

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