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Last updated: 14 Jul 2022

govuk-knowledge-graph-gcp: Terraform state transitions

Terraform tries not to delete or overwrite something that it didn't create in the first place. It does this by storing the current 'state' of objects that it did create. When an object is later removed from the config, but is still in the 'state', then Terraform will delete it. But if an object exists in reality and not in the 'state', then Terraform will leave it be.

graph LR
    A[N: config<br/>N: state<br/>N reality] -->|Nothing to do| B(N: config<br/>N state<br/>N: reality)
    C[Y: config<br/>N: state<br/>N reality] -->|Create| D(Y: config<br/>Y state<br/>Y: reality)
    E[N: config<br/>Y: state<br/>N reality] -->|Someone manually deleted it,<br/>and also removed it from the config.| F(?)
    G[N: config<br/>N: state<br/>Y reality] -->|Ignore| H(N: config<br/>N state<br/>Y: reality)
    I[Y: config<br/>Y: state<br/>N reality] -->|Recreate?<br/>Someone manually deleted it.| D
    K[Y: config<br/>N: state<br/>Y reality] -->|Ask the user to import it into the state.| D
    M[N: config<br/>Y: state<br/>Y reality] -->|Delete| N(N: config<br/>N state<br/>N: reality)
    O[Y: config<br/>Y: state<br/>Y reality] -->|Nothing to do| P(Y: config<br/>Y state<br/>Y: reality)