Copy a variable with envVarKey

envVarKey copies the value of a variable of a different service during the apply.

The apply reads the value of TOKEN in the service api.

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ferry.yaml

services:
  - type: worker
    name: worker
    envVars:
      - key: KEY
        fromService:
          type: web
          name: api
          envVarKey: TOKEN

envVarKey gives a copy, not a reference. A later change of the source variable reaches the copy only at the next apply.

envVarKey works only with services, not with datastores.

Where the value comes from

From the blueprint, when the other service has that key in its envVars.
If not, from the saved environment of the service that exists.
If no one has it, the apply leaves the variable with no value and gives a warning:

env var 'KEY' not copied: service 'api' has no variable 'TOKEN' yet

Reference properties

The property of fromDatabase or fromService tells which value of the target the variable gets.

How an apply works

An apply has four steps. Ferry writes nothing before the full file is valid.

Copy a variable with envVarKey

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Where the value comes from