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35 lines
1.9 KiB
Markdown
35 lines
1.9 KiB
Markdown
---
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title: "ADR: Frontend API design"
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---
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## Background
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Previous version of the Frontend API (known as proxy API) had memory and I/O issues when a large number of tokens was used.
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To better understand how it worked you need to know that Frontend API is Unleash Node SDK exposed over the API.
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Node SDK allows to plug in a custom repository so that it can fetch the toggles from a database instead of making remote HTTP calls.
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Every time a new Frontend API token was used we created a new SDK client with its own proxy repository. Proxy repository was fetching
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the flags for a project and environment extracted from a token.
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Every time there was a revision ID change (e.g. after some flag changed the status) the repository was updating itself.
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Since every token had a dedicated repository with 10 tokens we were making 10 DB calls on each change.
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What's more each repository kept its own copy of the flags. What it means in practice is that two different tokens with the same
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project and environments would store the same flags twice.
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## Decision
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To address these challenges, we came up with a new design:
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We decided to swap ProxyRepository with a drop-in replacement FrontendApiRepository. FrontendApiRepository doesn't store any flags on its own but always filters
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the flags that we keep in a GlobalFrontendApiCache. The cache stores all the flags and updates on every revision ID change.
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Consequences:
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* memory improvements: for a large number of tokens the memory footprint is reduced since we only store one copy of each flag in the cache and every repository
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filters the data that it needs for a given project and environment obtained from the token
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* I/O improvements: for a large number of tokens the number of DB calls is reduced to one per revision ID update since only the cache needs to be updated
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