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Fabro can use your project’s devcontainer configuration to set up sandbox environments. When enabled, Fabro resolves devcontainer.json from the repository, uses its Dockerfile to build the Daytona sandbox snapshot, runs lifecycle hooks inside the sandbox, and merges devcontainer environment variables into the sandbox environment.

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Enabling devcontainer support

Set devcontainer = true in the [sandbox] section of your run config:
run.toml
version = 1
graph = "workflow.fabro"

[sandbox]
provider = "daytona"
devcontainer = true
Fabro looks for .devcontainer/devcontainer.json in the repository root. If found, it extracts the Dockerfile, lifecycle commands, and environment variables from the configuration.

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What Fabro uses from devcontainer.json

FieldHow Fabro uses it
build.dockerfileUsed as the Dockerfile for the Daytona sandbox snapshot. A deterministic snapshot name is generated from a hash of the Dockerfile content.
onCreateCommandRuns inside the sandbox after it’s created
postCreateCommandRuns after onCreateCommand completes
postStartCommandRuns after the sandbox starts
containerEnvMerged into sandbox environment variables (TOML [sandbox.env] values take precedence on key collisions)
Lifecycle commands (onCreateCommand, postCreateCommand, postStartCommand) execute sequentially inside the sandbox. If any command fails, the run aborts before the workflow starts.

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Dockerfile limitations

Fabro detects and reports unsupported COPY and ADD instructions in devcontainer base Dockerfiles. These instructions reference files from the build context, which isn’t available when building Daytona snapshots. If your Dockerfile uses COPY or ADD, you’ll need to restructure it to use RUN commands that fetch files at build time (e.g., via curl or wget).

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Interaction with other sandbox settings

When devcontainer = true, the devcontainer Dockerfile overrides any snapshot.dockerfile setting in [sandbox.daytona]. Other Daytona settings (cpu, memory, disk, auto_stop_interval, labels) still apply. Environment variables from containerEnv in the devcontainer config are merged with [sandbox.env] from the TOML config. On key collisions, the TOML config wins.