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Optimized environments start in 1-3 minutes. Without optimization, startup can take 10+ minutes. This page covers the strategies that close that gap.

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Optimization strategies

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Use prebuilds

Prebuilds run your environment setup ahead of time: container builds, dependency installation, and startup tasks. When an environment starts, it loads from a prebuild snapshot instead of running setup from scratch. This is the single biggest optimization. Configure prebuilds to run on a daily schedule before your team or agents start work. You can also run a prebuild manually after important dependency or setup changes.

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Enable Dev Container image caching

For runners in your VPC, enable image caching to avoid rebuilding containers:
  • AWS runners: Caches built Dev Container images automatically
  • GCP runners: Supports image caching through Artifact Registry
Ona Cloud includes image caching by default.

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Optimize your Dockerfile

Structure your Dockerfile for caching efficiency:
  • Put stable dependencies first: System packages, build tools, and runtimes that rarely change should be early in the Dockerfile.
  • Put volatile dependencies last: Application dependencies that change frequently go at the end.
  • Use prebuilt base images: Push your base image to a registry and reference it in devcontainer.json.

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Use tasks for dynamic setup

For setup that must happen at runtime (database seeding, environment-specific config), use Tasks rather than baking everything into the image.

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Use one environment per task

Create a fresh environment for each piece of work rather than reusing environments across tasks. This matches how agents operate:
  1. Agent receives a task
  2. Agent starts a clean environment
  3. Agent completes the work and creates a PR
  4. Environment is discarded
This isolation gives you:
  • No state conflicts: Each task gets a clean slate
  • Parallel execution: Multiple agents work simultaneously without interference
  • Mistakes are free: If something goes wrong, discard the environment and start fresh
With the optimizations above, startup stays under a few minutes.

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Measure startup time

Track these metrics to identify bottlenecks:
  • Container build time: How long does the Dev Container image take to build?
  • Dependency installation: How long do startup tasks take to run?
  • Prebuild freshness: Are prebuilds running often enough to stay current?
If environments take more than 3 minutes to start, check your prebuild configuration first.