How an apply works

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

Parse. Ferry reads the YAML into services, datastores and env groups. It reads each plan into limits.

1 / 4

An apply can fail only in the first two steps. Then the server stays as it was.

Parse

An error in the structure stops the apply with a 400 error. The error gives the name of the entry:

service 'a': envVars[0] (A): needs a value, generateValue: true, fromDatabase, fromService or sync: false

A key that Ferry does not support and a plan that Ferry does not know only add warnings.

The validation of each entry comes before each write. If one entry is not valid, the full apply fails and Ferry writes nothing.

Then each resource gets a action. An update has a list of changes.

Ferry writes in the order of the dependencies. Then it starts the deploys and restarts: see What an apply deploys.

Copy a variable with envVarKey

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

What an apply deploys

After the writes, Ferry starts only the deploys and restarts that the changes need.