Add docs for fly-autoscaler #1583
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@benbjohnson Made some smaller fixes from the original draft but left comments for you about bigger changes. |
| - `FAS_CREATED_MACHINE_COUNT`: An [Expr](https://expr-lang.org/) expression to calculate the number of Machines to create or destroy. | ||
| - `FAS_STARTED_MACHINE_COUNT`: An [Expr](https://expr-lang.org/) expression to calculate the number of Machines to stop or start. |
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I see that there are still some MIN and MAX versions of FAS_CREATED_MACHINE_COUNT and FAS_STARTED_MACHINE_COUNT. Do we include these in the reference or do we just use the Expr expression to calculate these values internally?
| - `FAS_PROMETHEUS_QUERY`: The Prometheus query to run. | ||
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| ### Temporal collector |
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I see a FAS_TEMPORAL_QUERY variable, but it's not in the Fresh Produce or this doc? What is it and should we include it?
| - `FAS_CREATED_MACHINE_COUNT`: An [Expr](https://expr-lang.org/) expression to calculate the number of Machines to create or destroy. | ||
| - `FAS_STARTED_MACHINE_COUNT`: An [Expr](https://expr-lang.org/) expression to calculate the number of Machines to stop or start. | ||
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| ### Prometheus collector |
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I see a FAS_PROMETHEUS_TOKEN variable too. What is it and should we include it?
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| The metrics-based autoscaler scales an app's Machines based on any metric, such as pending work items or queue depth. Scaling on metrics other than requests or connections is useful for apps, like background workers, that aren't running web services. Apps with services that need to scale based on HTTP requests can use the built-in Fly Proxy [autostop/autostart feature](https://fly.io/docs/apps/autostart-stop/) for Machines. | ||
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| The autoscaler works by collecting metrics from different sources, such as Prometheus or Temporal, and computing the number of required Machines based on those metrics. This reconciliation process happens on a loop every 15 seconds by default. We use the [Expr language](https://expr-lang.org/) for defining target Machine counts, which gives a rich set of built-in arithmetic functions. |
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Should we say how you can change the reconciliation interval in the yml config? Can you use a combination of yaml config and env variables?
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@benbjohnson I'm going to publish as-is, since it's fairly complete, and we can revisit my questions when there's time. |
Summary of changes
Add docs for fly-autoscaler, the metrics-based autoscaler app.
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Related Fly.io community and GitHub links
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