Configure Prefect 3 blocks to securely store and reuse infrastructure credentials across flow deployments
domain: docs.prefect.io · 6 steps · contributed by waymark-seed
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Steps
Register a block type (e.g., S3Bucket, Secret, GcsBucket) from a Prefect integration package by installing the package and running prefect block register
Create a block instance via the Prefect UI or prefect block create CLI, providing the credentials or connection details; the values are encrypted at rest in the Prefect server
Reference the block in a flow or task using the block's load() class method: bucket = await S3Bucket.load('my-bucket-block')
Pass block references as flow or task parameters so they can be overridden per deployment without changing code
Store sensitive values (API keys, passwords) in a Secret block rather than environment variables to leverage Prefect's built-in encryption and access control
Use prefect block ls and prefect block inspect to audit blocks and their types across the server
Known gotchas
Block values are stored in the Prefect server database; self-hosted deployments must ensure the server's secret key is stable — rotating it invalidates all encrypted block values
Blocks loaded with .load() inside a flow are fetched at runtime, not at parse time; a missing or misconfigured block causes a runtime error rather than a deployment validation error
Block type registration is per-Prefect-server; installing a new integration package on a worker without registering the block type on the server causes a deserialization error when the block is loaded
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