Add docker-in-docker azure_dns_override flag (#200)

* Add docker-in-docker azure_dns_overrideflag

* Update install.sh

* clarify variable name

* update option name and description for `azureDnsAutoDetection`

* bump feature version
Co-authored-by: Josh Spicer <josh@joshspicer.com>

src/docker-in-docker/devcontainer-feature.json

 {
     "id": "docker-in-docker",
-    "version": "1.0.4",
+    "version": "1.0.5",
     "name": "Docker (Docker-in-Docker)",
     "documentationURL": "https://github.com/devcontainers/features/tree/main/src/docker-in-docker",
     "description": "Create child containers *inside* a container, independent from the host's docker instance. Installs Docker extension in the container along with needed CLIs.",
@@ -28,6 +28,11 @@
             ],
             "default": "v1",
             "description": "Default version of Docker Compose (v1 or v2)"
+        },
+        "azureDnsAutoDetection": {
+            "type": "boolean",
+            "default": true,
+            "description": "Allow automatically setting the dockerd DNS server when the installation script detects it is running in Azure"
         }
     },
     "entrypoint": "/usr/local/share/docker-init.sh",

src/docker-in-docker/install.sh

@@ -11,6 +11,7 @@
 DOCKER_VERSION=${VERSION:-"latest"} # The Docker/Moby Engine + CLI should match in version
 USE_MOBY=${MOBY:-"true"}
 DOCKER_DASH_COMPOSE_VERSION=${DOCKERDASHCOMPOSEVERSION:-"v1"} # v1 or v2
+AZURE_DNS_AUTO_DETECTION=${AZUREDNSAUTODETECTION:-"true"}
 
 ENABLE_NONROOT_DOCKER=${ENABLE_NONROOT_DOCKER:-"true"}
 USERNAME=${USERNAME:-"automatic"}
@@ -312,7 +313,7 @@ if [ "${ENABLE_NONROOT_DOCKER}" = "true" ]; then
 fi
 
 tee /usr/local/share/docker-init.sh > /dev/null \
-<< 'EOF'
+<< EOF
 #!/bin/sh
 #-------------------------------------------------------------------------------------------------------------
 # Copyright (c) Microsoft Corporation. All rights reserved.
@@ -321,6 +322,11 @@ tee /usr/local/share/docker-init.sh > /dev/null \
 
 set -e
 
+AZURE_DNS_AUTO_DETECTION=$AZURE_DNS_AUTO_DETECTION
+EOF
+
+tee -a /usr/local/share/docker-init.sh > /dev/null \
+<< 'EOF'
 dockerd_start="$(cat << 'INNEREOF'
     # explicitly remove dockerd and containerd PID file to ensure that it can start properly if it was stopped uncleanly
     # ie: docker kill <ID>
@@ -360,7 +366,7 @@ dockerd_start="$(cat << 'INNEREOF'
     # Handle DNS
     set +e
     cat /etc/resolv.conf | grep -i 'internal.cloudapp.net'
-    if [ $? -eq 0 ]
+    if [ $? -eq 0 ] && [ ${AZURE_DNS_AUTO_DETECTION} = "true" ]
     then
         echo "Setting dockerd Azure DNS."
         CUSTOMDNS="--dns 168.63.129.16"