Limit the number of sites the process manager keeps running by katinthehatsite · Pull Request #3887 · Automattic/studio

katinthehatsite · 2026-06-18T13:51:06Z

Related issues

Fixes STU-1841

How AI was used in this PR

It was used to plan and implement the feature

Proposed Changes

This PR limits the amount of sites that can be started at the same time to avoid draining memory. We can start:

24 native-php sites (24 × 1 = 24)
4 playground sites (4 × 6 = 24)
Or any mix, e.g. 3 playground + 6 native-php (18 + 6 = 24)

Testing Instructions

Pull the changes from this branch
Build CLI npm run cli:build
Run node apps/cli/dist/cli/main.mjs site stop --all
Start Studio with npm start
Try starting 5 Plaground sites and confirm that on the fifth one, you get the warning about the running limit as indicated on the screenshot above

Pre-merge Checklist

Have you checked for TypeScript, React or other console errors?

wpmobilebot · 2026-06-18T14:11:25Z

📊 Performance Test Results

Comparing 421d6db vs trunk

app-size

Metric	trunk	`421d6db`	Diff	Change
App Size (Mac)	1311.86 MB	1311.86 MB	+0.00 MB	⚪ 0.0%

site-editor

Metric	trunk	`421d6db`	Diff	Change
load	1097 ms	1117 ms	+20 ms	⚪ 0.0%

site-startup

Metric	trunk	`421d6db`	Diff	Change
siteCreation	6537 ms	6504 ms	33 ms	⚪ 0.0%
siteStartup	6563 ms	6578 ms	+15 ms	⚪ 0.0%

Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)

fredrikekelund

The basics are solid here 👍 Still, there are a few things I think we should tackle before landing this. Aside from the inline comments, I think we should also update apps/cli/commands/site/start.ts to write autoStart: false for the site if startWordPressServer throws.

fredrikekelund · 2026-06-23T07:31:10Z

+				throw new Error(
+					`CAPACITY_LIMIT_REACHED: Cannot start site — the weighted capacity limit of ${ MAX_WEIGHTED_CAPACITY } has been reached (current usage: ${ currentUsage }, requested: ${ weight }). Stop some running sites first.`
+				);


Suggested change

throw new Error(

`CAPACITY_LIMIT_REACHED: Cannot start site — the weighted capacity limit of ${ MAX_WEIGHTED_CAPACITY } has been reached (current usage: ${ currentUsage }, requested: ${ weight }). Stop some running sites first.`

);

const errorMessage =

runtime === SITE_RUNTIME_PLAYGROUND

? `Cannot start site. The maximum number of running sites has been reached (${ currentUsage }/${ MAX_WEIGHTED_CAPACITY }). Sandbox sites count as ${ weight } units. Stop some running sites first.`

: `Cannot start site. The maximum number of running sites has been reached (${ currentUsage }/${ MAX_WEIGHTED_CAPACITY }). Stop some running sites first.`;

throw new Error( `CAPACITY_LIMIT_REACHED: ${ errorMessage }` );

This message is displayed to users when starting a site using the CLI. I think we can simplify it along these lines. "Weighted capacity" doesn't mean much to a regular user.

Made adjustments in 4f1be5a

fredrikekelund · 2026-06-23T07:33:06Z

-		await Promise.allSettled( stoppedSites.map( ( site ) => startServer( site ) ) );
+		for ( const site of stoppedSites ) {
+			const { capacityLimitReached } = await startServer( site );
+			if ( capacityLimitReached ) {
+				break;
+			}
+		}


Again, this switches from parallel to sequential. I suggest reverting.

Reverted in https://github.com/Automattic/studio/pull/3887/commits

fredrikekelund · 2026-06-23T08:50:37Z

autoStart: false

Just noting that #3837 just landed, which changes where the autoStart props are stored.

katinthehatsite · 2026-06-23T12:37:02Z

Thanks for the review @fredrikekelund - I will take a look at the comments now.

…m:Automattic/studio into fix/limit-number-of-sites-process-manager

…umber-of-sites-process-manager

fredrikekelund

LGTM 👍 I pushed a fix for the thing I mentioned in my previous review about setting autoStart: false on sites that fail to start

katinthehatsite · 2026-06-24T12:16:14Z

LGTM 👍 I pushed a fix for the thing I mentioned in my previous review about setting autoStart: false on sites that fail to start

Thank you 🙇

Add cap for max sites

c647501

katinthehatsite self-assigned this Jun 18, 2026

katinthehatsite marked this pull request as draft June 18, 2026 13:51

Kateryna Kodonenko and others added 2 commits June 19, 2026 09:57

Fix linter

1b3c1fd

Merge branch 'trunk' into fix/limit-number-of-sites-process-manager

622bff2

katinthehatsite marked this pull request as ready for review June 19, 2026 08:28

katinthehatsite requested a review from a team June 19, 2026 08:28

fredrikekelund reviewed Jun 23, 2026

View reviewed changes

Remove redundant null coalescing

c418363

Kateryna Kodonenko added 8 commits June 23, 2026 14:44

Increase the amount of sites

a347871

Merge branch 'fix/limit-number-of-sites-process-manager' of github.co…

31e1f42

…m:Automattic/studio into fix/limit-number-of-sites-process-manager

Simplify error message

3c5e668

Apply suggestion

4f1be5a

Revert processing

ad7126d

Revert other changes

2e24fcb

Merge branch 'trunk' of github.com:Automattic/studio into fix/limit-n…

4f78b62

…umber-of-sites-process-manager

Start flag

a140e48

katinthehatsite requested a review from fredrikekelund June 23, 2026 13:28

Persist autoStart: false when a server fails to start

b415a44

fredrikekelund approved these changes Jun 24, 2026

View reviewed changes

Merge branch 'trunk' into fix/limit-number-of-sites-process-manager

421d6db

katinthehatsite merged commit 9fe8226 into trunk Jun 24, 2026
11 checks passed

katinthehatsite deleted the fix/limit-number-of-sites-process-manager branch June 24, 2026 12:33

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Limit the number of sites the process manager keeps running - #3887

Limit the number of sites the process manager keeps running#3887
katinthehatsite merged 14 commits into
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fix/limit-number-of-sites-process-manager

katinthehatsite commented Jun 18, 2026 •

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-				throw new Error(
-					`CAPACITY_LIMIT_REACHED: Cannot start site — the weighted capacity limit of ${ MAX_WEIGHTED_CAPACITY } has been reached (current usage: ${ currentUsage }, requested: ${ weight }). Stop some running sites first.`
-				);
+				const errorMessage =
+					runtime === SITE_RUNTIME_PLAYGROUND
+						? `Cannot start site. The maximum number of running sites has been reached (${ currentUsage }/${ MAX_WEIGHTED_CAPACITY }). Sandbox sites count as ${ weight } units. Stop some running sites first.`
+						: `Cannot start site. The maximum number of running sites has been reached (${ currentUsage }/${ MAX_WEIGHTED_CAPACITY }). Stop some running sites first.`;
+				throw new Error( `CAPACITY_LIMIT_REACHED: ${ errorMessage }` );

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Related issues

How AI was used in this PR

Proposed Changes

Testing Instructions

Pre-merge Checklist

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📊 Performance Test Results

app-size

site-editor

site-startup

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katinthehatsite commented Jun 18, 2026 •

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