Precedence for zonal shifts
There can be no more than one applied zonal shift at a given time. That is, only one practice run zonal shift, customer-initiated zonal shift, autoshift, or AWS FIS experiment for the resource. When a second zonal shift is started, ARC follows a precedence to determine which zonal shift type is in effect for a resource.
The general principle for precedence is that zonal shifts that you start as a customer take precedence over other shift types. However, be aware that a currently-running AWS-initiated practice run prevents you from starting an on-demand practice run.
To illustrate precedence in ARC, the following is how precedence works for example scenarios:
| Zonal shift type applied | Zonal shift type initiated | Result |
|---|---|---|
| AWS FIS experiment | Practice run | The practice run will fail to start, as the AWS FIS experiment takes precedence. |
| AWS FIS experiment | Manual zonal shift | The AWS FIS experiment will be canceled, and the manual zonal shift will be applied. |
| AWS FIS experiment | Zonal autoshift | The AWS FIS experiment will be canceled, and the zonal autoshift will be applied. |
| AWS FIS experiment | AWS FIS experiment | The initiated AWS FIS experiment will fail to start because there is an existing experiment running that triggered the AWS FIS autoshift action. |
| Practice run | Manual zonal shift | The practice run will be canceled and the outcome set to INTERRUPTED, and the zonal
shift will be applied. |
| Practice run | AWS FIS experiment | The practice run will be canceled and the outcome set to INTERRUPTED,
and the AWS FIS experiment will be applied. |
| Practice run | Zonal autoshift | The practice run will be canceled and the outcome set to INTERRUPTED,
and the zonal autoshift will be applied. |
| Manual zonal shift | Practice run | The practice run will fail to start. |
| Manual zonal shift | AWS FIS experiment | The AWS FIS experiment will fail to start, or fail if it's already in progress. |
| Manual zonal shift | Zonal autoshift | The zonal autoshift will be ACTIVE but not APPLIED on the
resource. The manual zonal shift takes precedence. |
| Zonal autoshift | AWS FIS experiment | The AWS FIS experiment will fail to start, or will fail if it's in progress. |
| Zonal autoshift | Manual zonal shift | The zonal autoshift will be ACTIVE but not APPLIED on the
resource. The manual zonal shift takes precedence. |
| Zonal autoshift | Practice run | The practice run will fail to start, as the zonal autoshift takes precedence. |
The traffic shift that is currently in effect for the resource has an applied zonal shift
status set to APPLIED. Only one shift is set to
APPLIED at any time. Other shifts that are in progress are
set to NOT_APPLIED, but remain with ACTIVE
status.
