---
title: "Devcontainers"
description: "Run Fabro workflows inside development containers"
---

Fabro can use your project's [devcontainer](https://containers.dev/) 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.

## Enabling devcontainer support

Set `devcontainer = true` in the `[run.sandbox]` section of your run config:

```toml title="run.toml"
_version = 1

[workflow]
graph = "workflow.fabro"

[run.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.

## What Fabro uses from devcontainer.json

| Field | How Fabro uses it |
|---|---|
| `build.dockerfile` | Used as the Dockerfile for the Daytona sandbox snapshot. A deterministic snapshot name is generated from a hash of the Dockerfile content. |
| `onCreateCommand` | Runs inside the sandbox after it's created |
| `postCreateCommand` | Runs after `onCreateCommand` completes |
| `postStartCommand` | Runs after the sandbox starts |
| `containerEnv` | Merged 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.

## 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`).

## 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.