Add LXD datasource (#1040)

Add DataSourceLXD which knows how to talk to the dev-lxd socket to
obtain all instance metadata API:
https://linuxcontainers.org/lxd/docs/master/dev-lxd.

This first branch is to deliver feature parity with the existing
NoCloud datasource which is currently used to intialize LXC instances
on first boot.

Introduce a SocketConnectionPool and LXDSocketAdapter to support
performing HTTP GETs on the following routes which are surfaced by the
LXD host to all containers:
http://unix.socket/1.0/meta-data
http://unix.socket/1.0/config/user.user-data
http://unix.socket/1.0/config/user.network-config
http://unix.socket/1.0/config/user.vendor-data
These 4 routes minimally replace the static content provided in the
following nocloud-net seed files:
/var/lib/cloud/nocloud-net/{meta-data,vendor-data,user-data,network-config}

The intent of this commit is to set a foundation for LXD socket
communication that will allow us to build network hot-plug features
by eventually consuming LXD's websocket upgrade route 1.0/events to
react to network, meta-data and user-data config changes over time.

In the event that no custom network-config is provided, default to the
same network-config definition provided by LXD to the NoCloud
network-config seed file.

Supplemental features above NoCloud datasource:
surface all custom instance data config keys via cloud-init query ds
which aids in discoverability of features/tags/labels as well as
conditional #cloud-config jinja templates operations based on custom
config options.
TBD: better cloud-init query support for dot-delimited keys

1 files changed, 7 insertions, 1 deletions

diff --git a/tools/ds-identify b/tools/ds-identify
index c2f710e9..30d4b0f6 100755
--- a/tools/ds-identify
+++ b/tools/ds-identify
@@ -123,7 +123,7 @@ DS_MAYBE=2
 DI_DSNAME=""
 # this has to match the builtin list in cloud-init, it is what will
 # be searched if there is no setting found in config.
-DI_DSLIST_DEFAULT="MAAS ConfigDrive NoCloud AltCloud Azure Bigstep \
+DI_DSLIST_DEFAULT="MAAS ConfigDrive NoCloud LXD AltCloud Azure Bigstep \
 CloudSigma CloudStack DigitalOcean Vultr AliYun Ec2 GCE OpenNebula OpenStack \
 OVF SmartOS Scaleway Hetzner IBMCloud Oracle Exoscale RbxCloud UpCloud VMware"
 DI_DSLIST=""
@@ -802,6 +802,12 @@ dscheck_MAAS() {
     return ${DS_NOT_FOUND}
 }
 
+# LXD datasource requires active /dev/lxd/sock
+# https://linuxcontainers.org/lxd/docs/master/dev-lxd
+dscheck_LXD() {
+    [ -S /dev/lxd/sock ] && return ${DS_FOUND} || return ${DS_NOT_FOUND}
+}
+
 dscheck_NoCloud() {
     local fslabel="cidata CIDATA" d=""
     case " ${DI_KERNEL_CMDLINE} " in