Webpack Build "heap out of memory" in CI

By Daniel Zoghalchali·Latchkey

A webpack build hit the V8 heap ceiling and aborted. Large dependency graphs, full source maps, and many parallel loaders push memory past the default heap in CI.

What this error means

The build fails with FATAL ERROR: ... JavaScript heap out of memory during bundling. Raising --max-old-space-size or trimming the build clears it with no config rewrite.

shell

<--- Last few GCs --->
FATAL ERROR: Reached heap limit Allocation failed - JavaScript heap out of memory
    at webpack/lib/Compilation.js

Common causes

Heap limit below the bundle size

Large apps with full source maps can exceed the default V8 heap during a production build.

Too much parallelism in loaders/minifiers

Parallel terser/babel work multiplies peak memory on a memory-tight runner.

How to fix it

Raise the V8 heap

Increase old-space memory below the runner RAM.

shell

NODE_OPTIONS="--max-old-space-size=4096" npx webpack --mode production

Slim the build or use a larger runner

Disable or reduce source maps in CI where not needed.
Cap minifier parallelism (terser-webpack-plugin parallel).
Build on a runner with more RAM for large apps.

How to prevent it

Set NODE_OPTIONS heap relative to runner RAM.
Keep CI source maps minimal.
Right-size runners for large bundles.

Frequently asked questions

What causes "Webpack heap OOM"?