Why Multi-Phase Runs?
Kurtosis runs its Starlark environment definitions in multiple phases.
This can create pitfalls for users not accustomed to the multi-phase idea. For example, the following code has a bug:
service = add_service(
config = struct(
image = "hello-world",
if service.ip_address == "22.214.171.124":
print("IP address matched")
if statement will never evaluate to true because
service.ip_address is in fact a future reference string that will never equal
We chose this multi-phase approach despite its complexity because it provides significant advantages over traditional scripting:
- Kurtosis can show the user the plan to execute before any changes are made.
- Kurtosis can validate the entire plan, saving the user from errors like container image typos, service name typos, and port typos before any changes are made.
- Kurtosis can optimize performance (e.g. downloading all container images before anything is executed, which is especially important on timing-sensitive tests).
In the future, the multi-phase approach will also:
- Give the user the power to have new services defined in the plan depend on existing services already running in the enclave.
- Give the user the power to remove and edit parts of the plan they don't like (useful when consuming third-party definitions).
- Allow users to "time-travel" through the plan, discovering what the environment will look like at any point during plan execution.
- Permit compiling a Kurtosis plan down to an idempotent, declarative format (e.g. Helm, Terraform, or Docker Compose).