Added shared keep-alive agent to external HTTP requests

[rmgpinto]

ref https://linear.app/ghost/issue/BER-3690

• got.extend in request-external.js had no agent configured, so every oEmbed / webmention / recommendation / image probe opened a fresh socket
• on a NAT-gatewayed VPC this holds the gateway at its connection-rate ceiling and causes port-collision drops that gateway sizing won't fix
• adds a shared http/https Agent (keepAlive: true, keepAliveMsecs: 60s, maxSockets: 256) wired into the central got instance
• routes probe-image-size through externalRequest.stream so the parallel cover/author/og/twitter/logo fetches from meta/image-dimensions.js reuse the same pool (and pick up the existing SSRF protections)

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 648ea51 and 2b6ec92.

📒 Files selected for processing (4)

• ghost/core/core/server/lib/image/image-size.js
• ghost/core/core/server/lib/image/image-utils.js
• ghost/core/core/server/lib/request-external.js
• ghost/core/test/unit/server/lib/image/image-utils.test.js

🚧 Files skipped from review as they are similar to previous changes (3)

• ghost/core/core/server/lib/image/image-size.js
• ghost/core/core/server/lib/request-external.js
• ghost/core/core/server/lib/image/image-utils.js

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Walkthrough

This PR improves image probing reliability and connection efficiency by introducing three coordinated changes: (1) adding shared keep-alive HTTP/HTTPS agents to the external request client so outbound connections are pooled and reused, (2) creating a local probe helper that uses the pooled client instead of probe-image-size's default client, and (3) refining the timeout mechanism in _probeImageSizeFromUrl to explicitly destroy streams on timeout expiry and clear timers via .finally() blocks.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main objective of the PR: adding a shared keep-alive agent to external HTTP requests, which directly addresses the core change across all modified files.
Description check	✅ Passed	The description is directly related to the changeset, providing clear context about the problem (socket exhaustion on NAT-gatewayed VPCs), the solution (shared keep-alive agents), and implementation details (SSRF protections and connection pooling).
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch keep-alive-optimization

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[Copilot]

Pull request overview

Introduces a shared keep-alive HTTP/HTTPS agent pool for outbound got requests in request-external.js to stop one-socket-per-request churn (which was saturating the NAT gateway's connection-rate limit). Image probing in probe-image-size is rewired through the same got instance so the parallel meta/image-dimensions fetches reuse the pool and pick up the existing SSRF protections; the outer "probe unresponsive" timeout now destroys the underlying stream so the pooled socket isn't leaked.

Changes:

• Add shared http.Agent / https.Agent (keep-alive, keepAliveMsecs: 60000, maxSockets/maxFreeSockets: 256) and wire them into the central got instance via gotOpts.agent.
• Replace direct use of probe-image-size in image-utils.js with a wrapper that streams the body through externalRequest.stream, exposing .stream on the returned promise.
• Update _probeImageSizeFromUrl to destroy the probe stream when the outer timeout wins, and clear the timeout in a finally to avoid leaks.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
ghost/core/core/server/lib/request-external.js	Adds shared keep-alive agents and registers them in the got.extend options.
ghost/core/core/server/lib/image/image-utils.js	Wraps probe-image-size over externalRequest.stream, exposing the underlying stream for cancellation.
ghost/core/core/server/lib/image/image-size.js	Reworks the probe/timeout race to destroy the stream on timeout and clear the timer on settle.

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[coderabbitai]

Actionable comments posted: 0