I changed CPU/RAM and nothing happened

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Symptom

You changed the CPU or RAM preset, saved, and the app carries on exactly as before — same performance, same memory limit.

Why

Resource limits are properties of the container, and a running container's limits can't be changed in place. The new values are stored as pending and applied when the container is next created.

The app will indicate that a restart is needed.

Fix

Restart the app. The new preset takes effect on the container that comes up.

The same is true of every other setting that belongs to the container rather than to your code — environment variables, ports, volumes, config files and the run command. All of them recreate the container when applied.

Which means: if you're making several changes, make them all and restart once rather than saving each one separately. Each save is an interruption.

The preset I want is greyed out

That's a different thing — it's above your account's limit, not pending. See Over limits.

It restarted but it's still slow

Confirm the change actually applied, then check whether resources were the problem at all:

  • Out of memory shows as exit code 137 in the app's Events. If you're seeing those, more RAM is the right fix.
  • CPU starvation is throttling, not slowness — your container gets a share of CPU time per short window and is paused when it's used up, so the symptom is latency spikes rather than uniform sluggishness.
  • Neither is common. Slow responses are more often a blocking call in the wrong place than a lack of resources, and adding CPU to a wasteful process just makes it fail more slowly.