Check the image is outdated and pop warning to pull the latest

aiidalab_launch/__main__.py

@@ -87,6 +87,29 @@ def callback(ctx, param, value):  # noqa: U100
     )(cmd)
 
 
+def image_is_latest(docker_client, image: str):
+    """Check if the local image has the same digest as the image
+    on remote registry.
+    """
+    try:
+        local_image = docker_client.images.get(image)
+    except docker.errors.ImageNotFound:
+        return False
+
+    try:
+        remote_image = docker_client.images.get_registry_data(image)
+    except docker.errors.APIError:
+        return False
+
+    # There is no need to check creation date of the image, since the once
+    # there is a new image with the same tag, the id will be different.
+    # We can not use image id, see https://windsock.io/explaining-docker-image-ids/
+    local_digest = local_image.attrs.get("RepoDigests")[0].split("@")[-1]
+    remote_digest = remote_image.attrs.get("Descriptor", {}).get("digest")
+
+    return local_digest == remote_digest
+
+
 @click.group(context_settings={"help_option_names": ["-h", "--help"]})
 @click.option(
     "-v",
@@ -350,6 +373,13 @@ async def _async_start(
         # use local image
         msg = f"Using local image '{profile.image}'."
 
+        # check if local image is outdated and pull latest version if so
+        if not image_is_latest(instance.client, profile.image):
+            click.secho(
+                "Warning! Local image is outdated, please run with --pull to update.",
+                fg="yellow",
+            )
+
     if instance.image is None:
         raise click.ClickException(
             f"Unable to find image '{profile.image}'. "