AWS Lambda SnapStart | Overview.

Here’s an overview of AWS Lambda SnapStart.

The concept: SnapStart

AWS Lambda SnapStart is a performance optimization for Java-based Lambdas (Java 11 & 17 runtimes) that cuts cold start time dramatically — often by up to 90%.

Instead of warming the environment from scratch on every cold start, AWS:

1. Initializes twtech function once ahead of time.
2. Takes a snapshot of the fully initialized runtime, code, and dependencies.
3. Reuses that frozen snapshot to instantly start new execution environments.

How SnapStart Works

1. Initialization Phase

• Happens once when twtech publishes a Lambda version.
• AWS:
• Starts a fresh environment.
• Runs the init code (class loading, static blocks, dependency injection frameworks like Spring, etc.).
• Stops before your Handler’s invoke() is called.

2. Snapshot

• AWS serializes the memory and execution state into a snapshot image.
• Includes:
• Loaded classes
• JIT-compiled code
• Initialized static variables
• Dependency graph

3. Restore Phase

• When a new execution environment is needed, AWS:
• Restores from the snapshot instead of re-running initialization.
• This skips the slow JVM boot, class loading, and dependency wiring steps.

Key Benefits

• Massive cold start reduction for Java Lambdas with heavy init times (Spring Boot, Micronaut, Quarkus, etc.).
• Consistent performance for burst traffic.

Limitations & Caveats

• Only works with Java 11/17 runtimes.
• Immutable init state:
• Any changes made during initialization are frozen in the snapshot.
• At restore time, twtech can’t rely on fresh data from init phase — it must fetch dynamic data at invocation time.
• No environment-variable changes after snapshot — if env vars change, twtech would need to republish the version.
• Ephemeral storage (/tmp) is not snapshotted.
• Some network connections (DB sockets, API sessions) may break after restore — use lazy initialization instead.

When to Use SnapStart

• Heavy frameworks with long cold starts.
• APIs that require low latency on first request.
• Functions triggered sporadically where cold starts matter.