I’ve been experimenting with deploying OpenStack using Nova/LXD (instead of Nova/KVM) for quite some time, using conjure-up as the deployment tool. It is simple, easy to set up and use and produces a usable OpenStack cluster.
However, I’ve been unable to run Docker inside a Nova instance (implemented as an LXD container) using an out-of-the-box installation deployed by conjure-up. The underlying reason is that the LXD container where nova-compute is hosted lacks some privileges. Also, inside this nova-compute container Nova/LXD spawns nested LXD containers, one for each Nova instance, which again lack some additional privileges required by Docker.
Short story, you can apply the docker LXD profile to both the nova-compute container and those nested LXD containers inside it where you want to run Docker, and Docker will run fine:
⟫ juju status nova-compute ⟫ juju status nova-compute Model Controller Cloud/Region Version SLA conjure-openstack-novalx-1d1 conjure-up-localhost-718 localhost/localhost 2.2-beta4 unsupported App Version Status Scale Charm Store Rev OS Notes lxd 2.0.9 active 1 lxd jujucharms 10 ubuntu neutron-openvswitch 10.0.0 active 1 neutron-openvswitch jujucharms 240 ubuntu nova-compute 15.0.2 active 1 nova-compute jujucharms 266 ubuntu Unit Workload Agent Machine Public address Ports Message nova-compute/0* active idle 4 10.0.8.61 Unit is ready lxd/0* active idle 10.0.8.61 Unit is ready neutron-openvswitch/0* active idle 10.0.8.61 Unit is ready Machine State DNS Inst id Series AZ Message 4 started 10.0.8.61 juju-59ffc3-4 xenial Running ...
From the previous output, notice how the nova-compute/0 unit is running in machine #4, and that the underlying LXD container is named juju-59ffc3-4. Now, let’s see the LXD profiles used by this container:
⟫ lxc info juju-59ffc3-4 | grep Profiles Profiles: default, juju-conjure-openstack-novalx-1d1
The docker LXD profile is missing from this container, and this will cause that any nested container trying to use Docker will fail. Entering the nova-compute/0 container, we see initially no nested containers. That is, since there are no Nova instances, there are no LXD containers. Remember that when using Nova/LXD, there is a 1:1 mapping between a Nova instance and an LXD container:
⟫ lxc exec juju-59ffc3-4 /bin/bash root@juju-59ffc3-4:~# lxc list +------+-------+------+------+------+-----------+ | NAME | STATE | IPV4 | IPV6 | TYPE | SNAPSHOTS | +------+-------+------+------+------+-----------+
Let’s spawn a Nova instance for testing:
⟫ juju ssh nova-cloud-controller/0 ubuntu@juju-59ffc3-13:~$ source novarc ubuntu@juju-59ffc3-13:~$ openstack server create --flavor m1.small --image xenial-lxd --nic net-id=ubuntu-net test1
Now, if we take a look inside the nova-compute/0 container, we will see a nested container:
⟫ juju ssh nova-compute/0 ubuntu@juju-59ffc3-4:~$ sudo -i root@juju-59ffc3-4:~# lxc list +-------------------+---------+-------------------+------+------------+-----------+ | NAME | STATE | IPV4 | IPV6 | TYPE | SNAPSHOTS | +-------------------+---------+-------------------+------+------------+-----------+ | instance-00000001 | RUNNING | 10.101.0.9 (eth0) | | PERSISTENT | 0 | +-------------------+---------+-------------------+------+------------+-----------+ root@juju-59ffc3-4:~# lxc info instance-00000001 | grep Profiles Profiles: instance-00000001
Here one can see that the nested container is using a profile named after the Nova instance. Let’s enter this nested container, install Docker and try to spawn a Docker container:
root@juju-59ffc3-4:~# lxc exec instance-00000001 /bin/bash root@test1:~# apt-get update ... root@test1:~# apt-get -y install docker.io ... root@test1:~# docker run -it ubuntu /bin/bash Unable to find image 'ubuntu:latest' locally latest: Pulling from library/ubuntu b6f892c0043b: Pull complete 55010f332b04: Pull complete 2955fb827c94: Pull complete 3deef3fcbd30: Pull complete cf9722e506aa: Pull complete Digest: sha256:382452f82a8bbd34443b2c727650af46aced0f94a44463c62a9848133ecb1aa8 Status: Downloaded newer image for ubuntu:latest docker: Error response from daemon: containerd: container not started.
Here we can see that Docker was unable to spawn the Docker container.
First thing we are going to try is to add the docker LXD profile to the nested container, the one hosting our Nova instance:
⟫ juju ssh nova-compute/0 ubuntu@juju-59ffc3-4:~$ sudo -i root@juju-59ffc3-4:~# lxc list +-------------------+---------+-------------------+------+------------+-----------+ | NAME | STATE | IPV4 | IPV6 | TYPE | SNAPSHOTS | +-------------------+---------+-------------------+------+------------+-----------+ | instance-00000001 | RUNNING | 10.101.0.5 (eth0) | | PERSISTENT | 0 | +-------------------+---------+-------------------+------+------------+-----------+ root@juju-59ffc3-4:~# lxc info instance-00000001 | grep Profiles Profiles: instance-00000001 root@juju-59ffc3-4:~# lxc profile apply instance-00000001 instance-00000001,docker Profile instance-00000001,docker applied to instance-00000001
Now, let’s try again to run a Docker container:
root@juju-59ffc3-4:~# lxc exec instance-00000001 /bin/bash root@test1:~# docker run -it ubuntu /bin/bash root@7fc441a9b0a5:/# uname -r 4.10.0-21-generic root@7fc441a9b0a5:/#
But this, besides being a manual process, it is not elegant. There’s another solution which requires no operation intervention. It consists of a Python code patch to the Nova/LXD driver that allows selectively adding additional LXD profiles to Nova containers:
$ juju ssh nova-compute/0
ubuntu@juju-59ffc3-4:~$ sudo -i
root@juju-59ffc3-4:~# patch -d/ -p0 << EOF
--- /usr/lib/python2.7/dist-packages/nova_lxd/nova/virt/lxd/config.py.orig 2017-06-07 19:41:47.685278274 +0000
+++ /usr/lib/python2.7/dist-packages/nova_lxd/nova/virt/lxd/config.py 2017-06-07 19:42:58.891624467 +0000
@@ -56,11 +56,17 @@
instance_name = instance.name
try:
+ # Profiles to be applied to the container
+ profiles = [str(instance.name)]
+ lxd_profiles = instance.flavor.extra_specs.get('lxd:profiles')
+ if lxd_profiles:
+ profiles += lxd_profiles.split(',')
+
# Fetch the container configuration from the current nova
# instance object
container_config = {
'name': instance_name,
- 'profiles': [str(instance.name)],
+ 'profiles': profiles,
'source': self.get_container_source(instance),
'devices': {}
}
EOF
root@juju-59ffc3-4:~# service nova-compute restart
Now, let’s create a new flavor named docker with the extra spec to include the docker LXD profile to all instances that rely on this flavor:
⟫ juju ssh nova-cloud-controller/0 ubuntu@juju-59ffc3-13:~$ source novarc ubuntu@juju-59ffc3-13:~$ openstack flavor create --disk 20 --vcpus 2 --ram 1024 docker ubuntu@juju-59ffc3-13:~$ openstack flavor set --property lxd:profiles=docker docker ubuntu@juju-59ffc3-13:~$ openstack server create --flavor docker --image xenial-lxd --nic net-id=ubuntu-net test2
Then, inside the nova-compute container:
⟫ juju ssh nova-compute/0 ubuntu@juju-59ffc3-4:~$ sudo -i root@juju-59ffc3-4:~# lxc list +-------------------+---------+--------------------------------+------+------------+-----------+ | NAME | STATE | IPV4 | IPV6 | TYPE | SNAPSHOTS | +-------------------+---------+--------------------------------+------+------------+-----------+ | instance-00000001 | RUNNING | 172.17.0.1 (docker0) | | PERSISTENT | 0 | | | | 10.101.0.9 (eth0) | | | | +-------------------+---------+--------------------------------+------+------------+-----------+ | instance-00000003 | RUNNING | 10.101.0.8 (eth0) | | PERSISTENT | 0 | +-------------------+---------+--------------------------------+------+------------+-----------+ root@juju-59ffc3-4:~# lxc info instance-00000003 | grep Profiles Profiles: instance-00000003, docker root@juju-59ffc3-4:~# lxc exec instance-00000003 /bin/bash root@test2:~# apt-get update ... root@test2:~# apt-get -y install docker.io ... root@test2:~# docker run -it ubuntu /bin/bash Unable to find image 'ubuntu:latest' locally latest: Pulling from library/ubuntu b6f892c0043b: Pull complete 55010f332b04: Pull complete 2955fb827c94: Pull complete 3deef3fcbd30: Pull complete cf9722e506aa: Pull complete Digest: sha256:382452f82a8bbd34443b2c727650af46aced0f94a44463c62a9848133ecb1aa8 Status: Downloaded newer image for ubuntu:latest root@fd74cfa04876:/# uname -r 4.10.0-21-generic root@fd74cfa04876:/#
So, that’s it. With this small patch, which enables support for the lxd:profiles extra spec, it is easier to allow Docker to run inside Nova instances hosted in LXD containers.
felipe-alfaro.com 
Thanks a lot. Really nice tutorial !!! By the way do you think we can use Docker image directly import to Nova-lxd ? I was trying various way on that. But it seems not work. Do you have any idea.