Serverless Functions

Also Known As

TL;DR

Explanation

Serverless (Lambda, Cloud Functions, Azure Functions) runs code in response to events (HTTP request, queue message, cron schedule) without provisioning or managing servers. Billing is per invocation and execution time — idle costs nothing. Cold starts add latency when a function hasn't run recently. Functions must be stateless — any persistent state lives in a database or cache. PHP is supported via custom runtimes (Bref) on AWS Lambda.

Diagram

flowchart LR
    REQ[HTTP Request] --> GW[API Gateway]
    GW -->|cold start or warm| FN[Function Instance<br/>PHP via Bref]
    FN --> EXEC[Execute handler<br/>100ms-3s]
    FN --> DB[(Database)]
    FN --> S3[(S3)]
    subgraph Scaling
        GW -->|concurrent requests| FN1[Instance 1]
        GW -->|concurrent requests| FN2[Instance 2]
        GW -->|concurrent requests| FN3[Instance N - auto]
    end
    INFO[Pay per invocation<br/>Zero idle cost<br/>Cold start: 200ms-2s]
style FN fill:#238636,color:#fff
style INFO fill:#1f6feb,color:#fff

Common Misconception

Why It Matters

Common Mistakes

• Storing state in the function's memory or filesystem — functions are ephemeral; use Redis or a database.
• Ignoring cold start latency — functions not invoked recently take 200-2000ms to initialise.
• Monolithic serverless functions — small, single-purpose functions scale and deploy independently.
• Not setting memory/timeout limits — unlimited execution time runs up costs on stuck functions.

Code Examples

// Stateful serverless — state lost between invocations:
$counter = 0; // Top-level 'global' variable
function handler($event) {
    global $counter;
    $counter++; // Resets to 0 on every cold start — not persistent
    return ['count' => $counter];
}

// Stateless — state in Redis:
function handler($event) {
    $redis = new Redis();
    $redis->connect(getenv('REDIS_HOST'));
    $count = $redis->incr('invocation_count');
    return ['count' => $count]; // Persists across invocations
}
// Bref (PHP on Lambda): composer require bref/bref

References

• ↗ https://bref.sh/
• ↗ https://aws.amazon.com/lambda/

Tags

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