Add example scripts for side-loading airgapped docker images

Related to https://gitlab.com/gitlab-org/gitlab/issues/11520

doc/topics/airgap/index.md

@@ -13,3 +13,61 @@ If you plan to deploy a GitLab instance on a physically-isolated and offline net
 Follow these best practices to use GitLab's features in an offline environment:
 
 - [Operating the GitLab Secure scanners in an offline environment](../../user/application_security/offline_deployments/index.md).
+
+## Loading Docker images onto your air-gapped host
+
+To use many GitLab features, including
+[security scans](../../user/application_security/index.md#working-in-an-offline-environment)
+and [Auto Devops](../autodevops/), the GitLab Runner must be able to fetch the
+relevant Docker images.
+
+The process for making these images available without direct access to the public internet
+involves downloading the images then packaging and transferring them to the air-gapped host.
+Here's an example of such a transfer:
+
+1. Download Docker images from public internet.
+1. Package Docker images as tar archives.
+1. Transfer images to air-gapped environment.
+1. Load transferred images into air-gapped Docker registry.
+
+### Example image packager script
+
+```sh
+#!/bin/bash
+set -ux
+
+# Specify needed analyzer images
+analyzers=${SAST_ANALYZERS:-"bandit eslint gosec"}
+gitlab=registry.gitlab.com/gitlab-org/security-products/analyzers/
+
+for i in "${analyzers[@]}"
+do
+  tarname="${i}_2.tar"
+  docker pull $gitlab$i:2
+  docker save $gitlab$i:2 -o ./analyzers/${tarname}
+  chmod +r ./analyzers/${tarname}
+done
+```
+
+### Example image loader script
+
+This example loads the images from a bastion host to an air-gapped host. In certain configurations,
+physical media may be needed for such a transfer:
+
+```sh
+#!/bin/bash
+set -ux
+
+# Specify needed analyzer images
+analyzers=${SAST_ANALYZERS:-"bandit eslint gosec"}
+registry=$GITLAB_HOST:4567
+
+for i in "${analyzers[@]}"
+do
+  tarname="${i}_2.tar"
+  scp ./analyzers/${tarname} ${GITLAB_HOST}:~/${tarname}
+  ssh $GITLAB_HOST "sudo docker load -i ${tarname}"
+  ssh $GITLAB_HOST "sudo docker tag $(sudo docker images | grep $i | awk '{print $3}') ${registry}/analyzers/${i}:2"
+  ssh $GITLAB_HOST "sudo docker push ${registry}/analyzers/${i}:2"
+done
+```