Output CloudFront-friendly headers for diffs #1098
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CloudFront needs a `Date` header to go with the `Last-Modified` and `ETag` headers from the `stale?` method, and works better still if we give it an actual cache age. This adds the `expires_in` helper which sets all the headers. I've also taken the strategy of setting a *relatively* short cache time but a much longer revalidation window when a stale response can be used, to balance concerns about updating the diff algorithm and effective long-term caching. I've also set a forever timeframe (100 years) if the request included a `?diff_version` query parameter (conceptually, you can say "I want a diff from an any algorithm newer than `diff_version=2023-01-01`" and accept a cached copy from an older algorithm rather than regenerating a new one.
Mr0grog
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Mr0grog
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that referenced
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Mar 30, 2023
As part of putting things to rest and saving costs, we are removing the Redis cache and relying on CloudFront to do enough caching for us to solve the same use case. See also edgi-govdata-archiving/web-monitoring-db#1098.
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This is part of web-monitoring#168 — the goal here is to make our diff cache less important so we can shrink it or even remove it (in favor of just having CloudFront do the job).
CloudFront needs a
Dateheader to go with theLast-ModifiedandETagheaders from thestale?method, and works better still if we give it an actual cache age. This adds theexpires_inhelper which sets all the headers. I've also taken the strategy of setting a relatively short cache time but a much longer revalidation window when a stale response can be used, to balance concerns about updating the diff algorithm and effective long-term caching.