http server sticky

[charlesfrye]

This PR adds an example that demonstrates the sticky routing behavior.

The text includes a link to an http_server example that will appear in a concurrent PR. I won't make this example discoverable on the marketing site until I have that one merged as well.

Type of Change

• New example for the GitHub repo
  • New example for the documentation site (Linked from a discoverable page, e.g. via the sidebar in /docs/examples)

Monitoring Checklist

• Example is configured for testing in the synthetic monitoring system, or lambda-test: false is provided in the example frontmatter and I have gotten approval from a maintainer
  • Example is tested by executing with modal run, or an alternative cmd is provided in the example frontmatter (e.g. cmd: ["modal", "serve"])
  • Example is tested by running the cmd with no arguments, or the args are provided in the example frontmatter (e.g. args: ["--prompt", "Formula for room temperature superconductor:"]
  • Example does not require third-party dependencies besides fastapi to be installed locally (e.g. does not import requests or torch in the global scope or other code executed locally)

Documentation Site Checklist

Content

• Example is documented with comments throughout, in a Literate Programming style
• All media assets for the example that are rendered in the documentation site page are retrieved from modal-cdn.com

Build Stability

• Example pins all dependencies in container images
  • Example pins container images to a stable tag like v1, not a dynamic tag like latest
    - [ ] Example specifies a python_version for the base image, if it is used. The demonstrated behavior is so fundamental that IMO we should expect it to work across many Python versions, so I am not pinning here.
  • Example pins all dependencies to at least SemVer minor version, ~=x.y.z or ==x.y, or we expect this example to work across major versions of the dependency and are committed to maintenance across those versions
    • Example dependencies with version < 1 are pinned to patch version, ==0.y.z

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no potential bugs to report.

View in Devin Review to see 4 additional findings.

[charlesfrye]

Sorry for the noise -- ended up with a failure that only happened in CI, probably because they are very smol machines. Could have replicated locally, but was lazy and just pushed repeatedly instead.

I (my coding agent) switched to including timeouts amount the expected errors, and we've now had two successes in a row after three failures in a row. Will review synmon to see if this shows up there, in which case this might need more attention.

@prbot approve

[modal-pr-review-automation]

Approved 👍. @molocule will follow-up review this.

[molocule]

thanks for writing this !!