Experience using Kolla Ansible to upgrade Openstack from Ocata to Queens

We made a decision to use Kolla-Ansible for Openstack management approximately a year ago and we’ve just gone through the process of upgrading from Ocata to Pike to Queens. Here we provide a few notes on the experience.

By way of some context: our system is a moderate sized system with 3 storage nodes, 7 compute nodes and 3 controllers configured in HA. Our systems were running CentOS 7.5 with a 17.05.0-ce docker engine and we were using the centos-binary Kolla containers. Being an academic institution, usage of our system peaks during term time – performing the upgrade during the summer meant that system utilization was modest. As we are lucky enough to have tolerant users, we were not excessively concerned with ensuring minimal system downtime.

We had done some homework on some test systems in different configurations and had obtained some confidence with the Kolla-Ansible Ocata-Pike-Queens upgrade – we even managed to ‘upgrade’ from a set of centos containers to ubuntu containers without problem. We had also done an upgrade on a smaller, newer system which is in use and it went smoothly. However, we still had a little apprehension when performing the upgrade on the larger system.

In general, we found Kolla Ansible good and we were able to perform the upgrade without too much difficulty. However, it is not an entirely hands-off operation and it did require some intervention for which good knowledge of both Openstack and Kolla was necessary.

Our workflow was straightforward, comprising of the following three stages

  • generate the three configuration files passwords.yml, globals.yml and multinode.ha,
  • pull down all containers to the nodes using kolla-ansible pull
  • perform the upgrade using kolla-ansible upgrade.

We generated the globals.yml and passwords.yml config files by copying the empty config files from the appropriate kolla-ansible git branch to our /etc/kolla directory, comparing them with the files used in the previous deploy and copying changes from the previous versions into the new config file. We used the approach described here to generate the correct passwords.yml file.

Pulling appropriate containers to all nodes was straightforward:

/opt/kolla-ansible/tools/kolla-ansible \
    -i /etc/kolla/multinode.ha pull

It can take a bit of time, but it’s sensible as it does not have any impact on the operational system and reduces the amount of downtime when upgrading.

We were then ready to perform the deployment. Rather than run the system through the entire upgrade process, we chose a more conservative approach in which we upgraded a single service at a time: this was to maintain a little more control over the process and to enable us to check that each service was operating correctly after upgrade. We performed this using commands such as:

/opt/kolla-ansible/tools/kolla-ansible \
    -i /etc/kolla/multinode.ha --tags "haproxy" upgrade

We stepped through the services in the same order as listed in the main Kolla-Ansible playbook, deploying the services one by one.

The two services that we were most concerned about were those pertaining to data storage, naturally: mariadb and ceph. We were quite confident that the other processes should not cause significant problems as they do not retain much important state.

Before we started…

We had some initial problems with docker python libraries installed on all of our nodes. The variant of the docker python library available via standard CentOS repos is too old. We had to resort to pip to install a new docker python library which worked with newer versions of Kolla-Ansible.

Ocata-Pike Upgrade

Deploying all the services for the Ocata-Pike upgrade was straightforward: we just ran through each of the services in turn and there were no specific issues. When performing some final testing, however, the compute nodes were unable to schedule new VMs as neutron was unable to attach a VIF to the OVS bridge. We had seen this issue before and we knew that putting the compute nodes through a boot cycle solves it – not a very clean approach, but it worked.

Pike-Queens Upgrade

The Pike-Queens upgrade was more complex and we encountered issues that we had not specifically seen documented anywhere. The issues were the following:

    • the mariadb upgrade failed – when the slave instances were restarted, they did not join the mariadb cluster and we ended up with a cluster with 0 nodes in the ‘JOINED’ state. The master node also ended up in an inoperational state.
      • We solved this using the well documented approach to bootstrapping a mariadb cluster – we have our own variant of it for the kolla mariadb containers, which is essentially a replica of the mariadb_recovery functionality provided by kolla
      • This did involve a syncing process of replicating all data from the bootstrap node on each of the slave nodes; in our case, this took 10 minutes
    • when the mariadb database sync’d and reached quorum, we noticed many errors associated with record field types in the logs – for this upgrade, it was necessary to perform a mysql_upgrade, which we had not seen documented anywhere
    • the ceph upgrade process was remarkably painless, especially given that this involved a transition from Ceph Jewel to Ceph Luminous. We did have the following small issues to deal with
      • We had to modify the configuration of the ceph cluster using ceph osd require-osd-release luminous
      • We had one small issue that the cluster was in the HEALTH_WARN status as one application did not have an appropriate tag – this was easily fixed using ceph osd pool application enable {pool-name} {application-name}
      • for reasons that are not clear to us, Luminous considered the status of the cluster to be somewhat suboptimal and moved over 50% of the objects in the cluster; Jewel had given no indication that a large amount of the cluster data needed to be moved
    • Upgrading the object store rendered it unusable: in this upgrade, the user which authenticates against keystone with privilege to manage user data for the object store changed from admin to ceph_rgw. However, this user was not added to the keystone and all requests to the object store failed. Adding this user to the keystone and giving this user appropriate access to the service project fixed the issue.
      • This was due to a change that was introduced in the Ocata release after we had performed our deployment and it only became visible to use after we performed the upgrade.

Apart from those issues, everything worked fine; we did note that the nova database upgrade/migration in the Pike-Queens cycle did take quite a long time (about 10 minutes) for our small cluster – for a very large configuration, it may be necessary to monitor this more closely.

Final remarks…

The Kolla-Ansible upgrade process worked well for our modest deployment and we are happy to recommend it as an Openstack management tool for environments of such scale with quite standard configurations, although even with an advanced tool such as Kolla-Ansible, it is essential to have a good understanding of both Openstack and Kolla before depending on it in a production system.

Setting up container based Openstack with OVN networking

OVN is a relatively new networking technology which provides a powerful and flexible software implementation of standard networking functionalities such as switches, routers, firewalls, etc. Importantly, OVN is distributed in the sense that the aforementioned network entities can be realized over a distributed set of compute/networking resources. OVN is tightly coupled with OVS, essentially being a layer of abstraction which sits above a set of OVS switches and realizes the above networking components across these switches in a distributed manner.

A number of cloud computing platforms and more general compute resource management frameworks are working on OVN support, including oVirt, Openstack, Kubernetes and Openshift – progress on this front is quite advanced. Interestingly and importantly, one dimension of the OVN vision is that it can act as a common networking substrate which could facilitate integration of more than one of the above systems, although the realization of that vision remains future work.

In the context of our work on developing an edge computing testbed, we set up a modest Openstack cluster, to emulate functionality deployed within an Enterprise Data Centre with OVN providing network capabilities to the cluster. This blog post provides a brief overview of the system architecture and notes some issues we had getting it up and running.

As our system is not a production system, providing High Availability (HA) support was not one of the requirements; consequently, it was not necessary to consider HA OVN mode. As such, it was natural to host the OVN control services, including the Northbound and Southbound DBs and the Northbound daemon (ovn-northd) on the Openstack controller node. As this is the node through which external traffic goes, we also needed to run an external facing OVS on this node which required its own OVN controller and local OVS database. Further, as this OVS chassis is intended for external traffic, it needed to be configured with ‘enable-chassis-as-gw‘.

We configured our system to use DHCP provided by OVN; consequently the neutron DHCP agent was no longer necessary, we removed this process from our controller node. Similarly, L3 routing was done within OVN meaning that the neutron L3 agent was no longer necessary. Openstack metadata support is implemented differently when OVN is used: instead of having a single metadata process running on a controller serving all metadata requests, the metadata service is deployed on each node and the OVS switch on each node routes requests to 169.254.169.254 to the local metadata agent; this then queries the nova metadata service to obtain the metadata for the specific VM.

The services deployed on the controller and compute nodes are shown in Figure 1 below.

Figure 1: Neutron containers with and without OVN

We used Kolla to deploy the system. Kolla does not currently have full support for OVN; however specific Kolla containers for OVN have been created (e.g. kolla/ubuntu-binary-ovn-controller:queens, kolla/ubuntu-binary-neutron-server-ovn:queens). Hence, we used an approach which augments the standard Kolla-ansible deployment with manual configuration of the extra containers necessary to get the system running on OVN.

As always, many smaller issues were encountered while getting the system working – we will not detail all these issues here, but rather focus on the more substantive issues. We divide these into three specific categories: OVN parameters which need to be configured, configuration specifics for the Kolla OVN containers and finally a point which arose due to assumptions made within Kolla that do not necessarily hold for OVN.

To enable OVN, it was necessary to modify the configuration of the OVS switches operating on all the nodes; the existing OVS containers and OVSDB could be used for this – the OVS version shipped with Kolla/Queens is v2.9.0 – but it was necessary to modify some settings. First, it was necessary to configure system-ids for all of the OVS chassis’ – we chose to select fixed UUIDs a priori and use these for each deployment such that we had a more systematic process for setting up the system but it’s possible to use a randomly generated UUID.

docker exec -ti openvswitch_vswitchd ovs-vsctl set open_vswitch . external-ids:system-id="$SYSTEM_ID"

On the controller node, it was also necessary to set the following parameters:

docker exec -ti openvswitch_vswitchd ovs-vsctl set Open_vSwitch . \
    external_ids:ovn-remote="tcp:$HOST_IP:6642" \
    external_ids:ovn-nb="tcp:$HOST_IP:6641" \
    external_ids:ovn-encap-ip=$HOST_IP external_ids:ovn-encap type="geneve" \
    external-ids:ovn-cms-options="enable-chassis-as-gw"

docker exec openvswitch_vswitchd ovs-vsctl set open . external-ids:ovn-bridge-mappings=physnet1:br-ex

On the compute nodes this was necessary:

docker exec -ti openvswitch_vswitchd ovs-vsctl set Open_vSwitch . \
    external_ids:ovn-remote="tcp:$OVN_SB_HOST_IP:6642" \
    external_ids:ovn-nb="tcp:$OVN_NB_HOST_IP:6641" \
    external_ids:ovn-encap-ip=$HOST_IP \
    external_ids:ovn-encap-type="geneve"

Having changed the OVS configuration on all the nodes, it was then necessary to get the services operational on the nodes. There are two specific aspects to this: modifying the service configuration files as necessary and starting the new services in the correct way.

Not many changes to the service configurations were required. The primary changes related to ensuring the the OVN mechanism driver was used and letting neutron know how to communicate with OVN. We also used the geneve tunnelling protocol in our deployment and this required the following configuration settings:

  • For the neutron server OVN container
    • ml2_conf.ini
              mechanism_drivers = ovn
       	type_drivers = local,flat,vlan,geneve
       	tenant_network_types = geneve
      
       	[ml2_type_geneve]
       	vni_ranges = 1:65536
       	max_header_size = 38
      
       	[ovn]
       	ovn_nb_connection = tcp:172.30.0.101:6641
       	ovn_sb_connection = tcp:172.30.0.101:6642
       	ovn_l3_scheduler = leastloaded
       	ovn_metadata_enabled = true
      
    • neutron.conf
              core_plugin = neutron.plugins.ml2.plugin.Ml2Plugin
       	service_plugins = networking_ovn.l3.l3_ovn.OVNL3RouterPlugin
      
  • For the metadata agent container (running on the compute nodes) it was necessary to configure it to point at the nova metadata service with the appropriate shared key as well as how to communicate with OVS running on each of the compute nodes
            nova_metadata_host = 172.30.0.101
     	metadata_proxy_shared_secret = <SECRET>
     	bridge_mappings = physnet1:br-ex
     	datapath_type = system
     	ovsdb_connection = tcp:127.0.0.1:6640
     	local_ip = 172.30.0.101
    

For the OVN specific containers – ovn-northd, ovn-sb and ovn-nb databases, it was necessary to ensure that they had the correct configuration at startup; specifically, that they knew how to communicate with the relevant dbs. Hence, start commands such as

/usr/sbin/ovsdb-server /var/lib/openvswitch/ovnnb.db -vconsole:emer -vsyslog:err -vfile:info --remote=punix:/run/openvswitch/ovnnb_db.sock --remote=ptcp:$ovnnb_port:$ovsdb_ip --unixctl=/run/openvswitch/ovnnb_db.ctl --log-file=/var/log/kolla/openvswitch/ovsdb-server-nb.log

were necessary (for the ovn northbound database) and we had to modify the container start process accordingly.

It was also necessary to update the neutron database to support OVN specific versioning information: this was straightforward using the following command:

docker exec -ti neutron-server-ovn_neutron_server_ovn_1 neutron-db-manage upgrade heads

The last issue which we had to overcome was that Kolla and neutron OVN had slightly different views regarding the naming of the external bridges. Kolla-ansible configured a connection between the br-ex and br-int OVS bridges on the controller node with port names phy-br-ex and int-br-ex respectively. OVN also created ports with the same purpose but with different names patch-provnet-<UUID>-to-br-int and patch-br-int-to-provonet-<UUID>; as these ports had the same purpose, our somewhat hacky solution was to manually remove the the ports created in the first instance by Kolla-ansible.

Having overcome all these steps, it was possible to launch a VM which had external network connectivity and to which a floating IP address could be assigned.

Clearly, this approach is not realistic for supporting a production environment, but it’s an appropriate level of hackery for a testbed.

Other noteworthy issues which arose during this work include the following:

  • Standard docker apparmor configuration in ubuntu is such that mount cannot be run inside containers, even if they have the appropriate privileges. This has to be disabled or else it is necessary to ensure that the containers do not use the default docker apparmor profile.
  • A specific issue with mounts inside a container which resulted in the mount table filling up with 65536 mounts and rendering the host quite unusable (thanks to Stefan for providing a bit more detail on this) – the workaround was to ensure that /run/netns was bind mounted into the container.
  • As we used geneve encapsulation, geneve kernel modules had to be loaded
  • Full datapath NAT support is only available for linux kernel 4.6 and up. We had to upgrade the 4.4 kernel which came with our standard ubuntu 16.04 environment.

This is certainly not a complete guide to how to get Openstack up and running with OVN, but may be useful to some folks who are toying with this. In future, we’re going to experiment with extending OVN to an edge networking context and will provide more details as this work evolves.