feat(builder): detect and use overlay as graph driver if supported

Author: carmstrong

builder/image/bin/boot

@@ -53,8 +53,15 @@ CONFD_PID=$!
 # remove any pre-existing docker.sock
 test -e /var/run/docker.sock && rm -f /var/run/docker.sock
 
+# force overlay if it's supported
+mkdir --parents --mode=0700 /
+fstype=$(findmnt --noheadings --output FSTYPE --target /)
+if [[ "$fstype" == "overlay" ]]; then
+	DRIVER_OVERRIDE="--storage-driver=overlay"
+fi
+
 # spawn a docker daemon to run builds
-docker -d --bip=172.19.42.1/16 --insecure-registry 10.0.0.0/8 --insecure-registry 172.16.0.0/12 --insecure-registry 192.168.0.0/16 --insecure-registry 100.64.0.0/10 &
+docker -d --bip=172.19.42.1/16 $DRIVER_OVERRIDE --insecure-registry 10.0.0.0/8 --insecure-registry 172.16.0.0/12 --insecure-registry 192.168.0.0/16 --insecure-registry 100.64.0.0/10 &
 DOCKER_PID=$!
 
 # wait for docker to start

contrib/coreos/user-data.example

@@ -89,13 +89,14 @@ coreos:
       ExecStartPre=/usr/sbin/modprobe nf_conntrack
       ExecStart=/bin/sh -c "sysctl -w net.netfilter.nf_conntrack_max=262144"
   - name: load-overlay-module.service
+    command: start
     content: |
       [Unit]
       Description=Load overlay module before docker start
       Before=docker.service
 
       [Service]
-      ExecStart=/bin/bash -c "modprobe overlay"
+      ExecStart=/bin/bash -c "lsmod | grep overlay || modprobe overlay"
 write_files:
   - path: /etc/deis-release
     content: |