3.3 Canister snapshots
A canister is managed by controllers, which can be:
A single developer identity.
Multiple developer identities.
Another canister.
One method of recovery is rolling the canister back to a previously saved snapshot (if one exists).
What are canister snapshots?
A canister contains compiled Wasm code and data such as the canister ID, settings, and Wasm memory. If a canister stops functioning, traps, or needs to be restored to a previous state, developers can use canister snapshots. Snapshots save the current:
- Stable memory.
- Heap memory.
- Wasm module.
- Canister metadata.
Snapshots can only be taken when a canister is stopped, and only controllers are permitted to create, load, or delete snapshots. If a canister has no controller and no access to the controller identities can be regained, there is no supported method to recover the canister.
Creating a snapshot
To create a snapshot:
dfx canister stop <canister-name>
dfx canister snapshot create <canister-name>
Only 10 snapshots can be stored per canister.
To create a snapshot on the mainnet, add --network ic to both commands.
To list existing snapshots:
dfx canister snapshot list <canister-name>
Loading a snapshot
To restore a canister from a saved snapshot:
dfx canister stop <canister-name>
dfx canister snapshot load <canister-name> <snapshot-id>
This will overwrite the canister’s current code and data. Any changes made since the snapshot was taken will be lost.
Deleting a snapshot
To delete a snapshot:
dfx canister snapshot delete <canister-name> <snapshot-id>