Principle:MaterializeInc Materialize Composition Execution
| Knowledge Sources | Container orchestration patterns, Docker Compose, ephemeral testing environments |
|---|---|
| Domains | Test Execution, Container Orchestration, Reproducible Environments, CI Infrastructure |
| Last Updated | 2026-02-08 |
Overview
Composition execution is the principle of running tests in isolated, ephemeral Docker Compose environments to ensure reproducibility, dependency isolation, and consistent behavior across developer machines and CI.
Description
Testing distributed systems like databases requires coordinating multiple services: the database itself, source connectors, sink connectors, load generators, and test drivers. Managing these services manually is error-prone and non-reproducible. Container-orchestrated test execution addresses this by defining each test environment as a Docker Compose composition, where:
- Each service runs in its own container with a well-defined image, configuration, and network identity.
- The composition file declares all services, their dependencies, ports, volumes, and environment variables.
- A test driver service (the runner) executes the test logic, interacting with the other services over the Docker network.
- The entire environment is ephemeral: created before the test, torn down after the test, with no state leaking between test runs.
This approach provides several key benefits:
- Reproducibility: The exact same container images and configurations run in CI and on developer machines. There are no "works on my machine" issues caused by differing local installations.
- Isolation: Tests run in their own network namespace. Multiple tests can run in parallel on the same host without port conflicts or shared state.
- Dependency Management: Each test declares exactly which services it needs. The orchestration layer handles starting them in the correct order and waiting for health checks.
- One-off Command Execution: Beyond long-running services, the orchestration layer supports running one-off commands in a service container. This is useful for test drivers that run a command, check its exit code, and capture its output.
The one-off command pattern is particularly important: the test framework needs to run a command inside a container with the full service environment available, capture its stdout/stderr, and propagate its exit code back to the CI system. This requires careful handling of container lifecycle (build, create, run, remove) and I/O streams (capture, print, or both).
Usage
Apply container-orchestrated test execution when:
- Tests require multiple interacting services (databases, message queues, connectors).
- Reproducibility across environments is critical.
- Tests should be isolated from each other and from the host system.
- The CI system needs to run tests in parallel across multiple agents.
- Test environments need to be created and destroyed programmatically.
Theoretical Basis
The theoretical basis for composition execution draws from several areas:
Environment Isolation: Linux namespaces and cgroups (the foundation of containers) provide process, network, and filesystem isolation. Docker Compose layers a declarative service definition on top, allowing multi-container environments to be specified as data (YAML) rather than imperative scripts.
Reproducible Builds: By pinning container images to specific versions or content-addressed tags, the test environment becomes a function of the source code. Any commit can recreate the exact test environment that was used in CI.
Service Orchestration: Docker Compose handles the directed acyclic graph of service dependencies, starting services in topological order and performing health checks before marking them as ready. This ensures that test drivers do not start before their dependencies are available.
One-off Command Pattern: The docker compose run command creates a new container from a service definition, runs a single command, and exits. This is the standard pattern for executing test commands in an orchestrated environment. Key considerations include:
- Entrypoint override: Allows running arbitrary commands in a container whose image has a default entrypoint.
- Environment injection: Additional environment variables can be passed at runtime without modifying the composition file.
- Output capture: stdout and stderr can be captured programmatically for assertion checking or artifact collection.
- Exit code propagation: The container's exit code must be propagated to the caller for pass/fail determination.