Fix: improve Docker startup and compose validation

[austin047]

• Set DOCKER_HOST from config to environment and verify Docker is reachable at startup
• Update config.example deployments_path to ./deployment
• Create deployments directory on startup if not exist; fail fast if Docker is unavailable
• Use the Default docker_socket from the Docker client env when unset
• Validate compose in updateDeployment via Docker Compose config
• Add moby/moby docker client dependency for platform socket detection

[sourceant]

Code Review Summary

This PR improves the robustness of the Flatrun Agent by ensuring Docker is reachable at startup and adding schema validation for Docker Compose files using the CLI.

🚀 Key Improvements

• Added moby/moby client for dynamic Docker host detection.
• Implemented ensureDockerReachable to fail-fast if the daemon is unavailable.
• Added comprehensive tests for Compose validation.
• Auto-creates the deployments directory if missing.

💡 Minor Suggestions

• Avoid using os.Setenv for DOCKER_HOST; prefer passing the socket to the client constructor.
• Tighten permissions on temporary files used for validation.

[sourceant]

Review complete. See the overview comment for a summary.

[sourceant]

Using exec.Command("docker", "info") relies on the docker CLI being installed in the PATH. Since you've added the moby/moby client dependency, it is more efficient and reliable to check connectivity using the library's Ping() or Info() methods instead of spawning a shell process.

Suggested change

	}
	func ensureDockerReachable(socket string) {
	ctx := context.Background()
	cli, err := client.NewClientWithOpts(client.WithHost(socket), client.WithAPIVersionNegotiation())
	if err != nil {
	log.Fatalf("Failed to create Docker client: %v", err)
	}
	defer cli.Close()
	if _, err := cli.Ping(ctx); err != nil {
	log.Fatalf("Docker is not reachable: %v", err)
	}
	}

[sourceant]

Closing the file before deleting it is safer on some operating systems (like Windows). Also, consider using defer os.Remove(tmp.Name()) immediately after creation to ensure cleanup even if subsequent steps fail.

Suggested change

	func validateComposeWithCLI(content string) error {
	tmp, err := os.CreateTemp("", "compose-*.yml")
	if err != nil {
	log.Printf("Warning: skipping CLI validation, failed to create temp file: %v", err)
	return nil
	}
	defer os.Remove(tmp.Name())
	defer tmp.Close()

[sourceant]

Review complete. See the overview comment for a summary.

[sourceant]

Setting DOCKER_HOST globally via os.Setenv can cause side effects if other parts of the application or third-party libraries expect a different environment. Since you've already added the Moby client, it is better to pass the socket explicitly to constructors rather than relying on global environment variables.

Suggested change

	os.Setenv("DOCKER_HOST", cfg.DockerSocket)
	ensureDockerReachable(cfg.DockerSocket)

[sourceant]

Creating a new client just to detect the default host is slightly heavy. Note that client.FromEnv will look at the DOCKER_HOST environment variable first. Ensure this fallback logic matches the expected behavior if the agent is running inside a container.

Suggested change

	apiClient, err := client.New(client.FromEnv)
	cli, err := client.NewClientWithOpts(client.FromEnv, client.WithAPIVersionNegotiation())
	if err == nil {
	cfg.DockerSocket = cli.DaemonHost()
	cli.Close()
	} else {
	cfg.DockerSocket = "unix:///var/run/docker.sock"
	}