Code At The Edge
Edge functions run small pieces of code in POPs near users, rewriting requests, adding headers, or assembling responses. Because they run on demand, the first invocation may pay a startup cost called a cold start.
What Causes A Cold Start
When no warm instance exists for a function, the platform must prepare one.
- Allocate an isolated runtime.
- Load and parse the function code.
- Initialize global state and connections.
This setup time is added to that first request. A warm start reuses an already prepared instance and skips this work.
Why Edge Cold Starts Are Smaller
Edge platforms often use lightweight isolates rather than full containers or virtual machines.
- Isolates share one runtime process, so spinning one up is cheap.
- Startup can be milliseconds rather than seconds.
- Many functions coexist with low memory each.
This makes cold starts far less painful than in traditional server environments, though not free.
Reducing The Impact
- Keep the function small with few heavy dependencies.
- Defer expensive initialization until it is actually needed.
- Rely on traffic to keep instances warm in busy regions.
Key idea
A cold start is the setup cost of preparing a fresh edge function instance, kept small by lightweight isolates and reduced further by lean code and deferred initialization.