Add support for entrypoint.

Signed-off-by: Shishir Mahajan <smahajan@roblox.com>

README.md

@@ -95,6 +95,7 @@ More detailed instructions are in the [`example README.md`](https://github.com/R
 | **image** | string | yes | OCI image (docker is also OCI compatible) for your container. |
 | **command** | string | no | Command to override command defined in the image. |
 | **args** | []string | no | Arguments to the command. |
+| **entrypoint** | string | no | Overwrite the default ENTRYPOINT of the image. |
 | **cwd** | string | no | Specify the current working directory for your container process. If the directory does not exist, one will be created for you. |
 | **privileged** | bool | no | Run container in privileged mode. Your container will have all linux capabilities when running in privileged mode. |
 | **host_dns** | bool | no | Default (`true`). By default, a container launched using `containerd-driver` will use host `/etc/resolv.conf`. This is similar to [`docker behavior`](https://docs.docker.com/config/containers/container-networking/#dns-services). However, if you don't want to use host DNS, you can turn off this flag by setting `host_dns=false`. |

containerd/containerd.go

@@ -76,14 +76,16 @@ func (d *Driver) pullImage(imageName string) (containerd.Image, error) {
 }
 
 func (d *Driver) createContainer(containerConfig *ContainerConfig, config *TaskConfig) (containerd.Container, error) {
-	if config.Command == "" && len(config.Args) > 0 {
+	if config.Command != "" && config.Entrypoint != "" {
-		return nil, fmt.Errorf("Command is empty. Cannot set --args without --command.")
+		return nil, fmt.Errorf("Both command and entrypoint are set. Only one of them needs to be set.")
 	}
 
-	// Command set by the user, to override entrypoint or cmd defined in the image.
+	// Entrypoint or Command set by the user, to override entrypoint or cmd defined in the image.
 	var args []string
 	if config.Command != "" {
 		args = append(args, config.Command)
+	} else if config.Entrypoint != "" {
+		args = append(args, config.Entrypoint)
 	}
 
 	// Arguments to the command set by the user.
@@ -93,7 +95,11 @@ func (d *Driver) createContainer(containerConfig *ContainerConfig, config *TaskC
 
 	var opts []oci.SpecOpts
 
-	opts = append(opts, oci.WithImageConfigArgs(containerConfig.Image, args))
+	if config.Entrypoint != "" {
+		opts = append(opts, oci.WithProcessArgs(args...))
+	} else {
+		opts = append(opts, oci.WithImageConfigArgs(containerConfig.Image, args))
+	}
 
 	if !d.config.AllowPrivileged && config.Privileged {
 		return nil, fmt.Errorf("Running privileged jobs are not allowed. Set allow_privileged to true in plugin config to allow running privileged jobs.")

containerd/driver.go

@@ -103,6 +103,7 @@ var (
 			hclspec.NewLiteral("true"),
 		),
 		"extra_hosts":     hclspec.NewAttr("extra_hosts", "list(string)", false),
+		"entrypoint":      hclspec.NewAttr("entrypoint", "string", false),
 		"seccomp":         hclspec.NewAttr("seccomp", "bool", false),
 		"seccomp_profile": hclspec.NewAttr("seccomp_profile", "string", false),
 		"readonly_rootfs": hclspec.NewAttr("readonly_rootfs", "bool", false),
@@ -161,6 +162,7 @@ type TaskConfig struct {
 	Privileged     bool     `codec:"privileged"`
 	HostDNS        bool     `codec:"host_dns"`
 	ExtraHosts     []string `codec:"extra_hosts"`
+	Entrypoint     string   `codec:"entrypoint"`
 	ReadOnlyRootfs bool     `codec:"readonly_rootfs"`
 	HostNetwork    bool     `codec:"host_network"`
 	Mounts         []Mount  `codec:"mounts"`