Node "FATAL ERROR: … Allocation failed" in CI - Tune V8 Memory for the Runner

A FATAL ERROR: ... Allocation failed in CI is V8 unable to grow memory for the workload on a constrained runner. Beyond raising the old-space heap, tuning the young-generation semi-space and runner memory together matters in CI.

What this error means

A CI build or test run aborts with FATAL ERROR: ... Allocation failed - JavaScript heap out of memory (or a process-out-of-memory abort). It passes on a beefier machine but fails on the smaller CI runner - a memory-fit problem specific to the runner.

<--- Last few GCs --->
[1:0x...]  Mark-Compact ... allocation failure
FATAL ERROR: MarkCompactCollector: young object promotion failed
Allocation failed - JavaScript heap out of memory

Common causes

The CI runner has less memory than the build needs

A build/test that fits on a developer machine exceeds a small CI runner’s memory, and V8 cannot allocate, aborting fatally.

Defaults not tuned for a high-allocation workload

Workloads that churn many short-lived objects thrash the young generation; the default semi-space and heap sizes are not tuned for the runner, so GC cannot keep up.

How to fix it

Tune V8 for the runner’s memory

Set the old-space heap below runner RAM and enlarge the semi-space for high-allocation builds.

# fit heap under runner memory; widen young-gen for churn-heavy builds
NODE_OPTIONS="--max-old-space-size=3072 --max-semi-space-size=64" npm run build
# in a workflow:
env:
  NODE_OPTIONS: --max-old-space-size=3072 --max-semi-space-size=64

Cut peak memory and/or size up the runner

1. Lower test parallelism and disable CI source maps.
2. Split a giant build into smaller workspace builds.
3. Move to a runner with more RAM if the workload genuinely needs it.

How to prevent it

• Set NODE_OPTIONS memory flags relative to the runner’s RAM.
• Right-size the CI runner for the heaviest build/test.
• Track build memory so growth is caught before it fails CI.

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