Downtime, whether planned or unscheduled, is a certainty when running a cloud. This chapter aims to provide useful information for dealing proactively, or reactively, with these occurrences. maintenance/debugging troubleshooting

The cloud controller and storage proxy are very similar to each other when it comes to expected and unexpected downtime. One of each server type typically runs in the cloud, which makes them very noticeable when they are not running. For the cloud controller, the good news is if your cloud is using the FlatDHCP multi-host HA network mode, existing instances and volumes continue to operate while the cloud controller is offline. For the storage proxy, however, no storage traffic is possible until it is back up and running.

One way to plan for cloud controller or storage proxy maintenance is to simply do it off-hours, such as at 1 a.m. or 2 a.m. This strategy affects fewer users. If your cloud controller or storage proxy is too important to have unavailable at any point in time, you must look into high-availability options. cloud controllers planned maintenance of maintenance/debugging cloud controller planned maintenance

All in all, just issue the "reboot" command. The operating system cleanly shuts down services and then automatically reboots. If you want to be very thorough, run your backup jobs just before you reboot. maintenance/debugging rebooting following storage storage proxy maintenance reboot cloud controller or storage proxy cloud controllers rebooting

After a cloud controller reboots, ensure that all required services were successfully started. The following commands use ps and grep to determine if nova, glance, and keystone are currently running: # ps aux | grep nova- # ps aux | grep glance- # ps aux | grep keystone # ps aux | grep cinder Also check that all services are functioning. The following set of commands sources the openrc file, then runs some basic glance, nova, and openstack commands. If the commands work as expected, you can be confident that those services are in working condition: # source openrc # glance index # nova list # openstack project list For the storage proxy, ensure that the Object Storage service has resumed: # ps aux | grep swift Also check that it is functioning: # swift stat

The cloud controller could completely fail if, for example, its motherboard goes bad. Users will immediately notice the loss of a cloud controller since it provides core functionality to your cloud environment. If your infrastructure monitoring does not alert you that your cloud controller has failed, your users definitely will. Unfortunately, this is a rough situation. The cloud controller is an integral part of your cloud. If you have only one controller, you will have many missing services if it goes down. cloud controllers total failure of maintenance/debugging cloud controller total failure To avoid this situation, create a highly available cloud controller cluster. This is outside the scope of this document, but you can read more in the OpenStack High Availability Guide. The next best approach is to use a configuration-management tool, such as Puppet, to automatically build a cloud controller. This should not take more than 15 minutes if you have a spare server available. After the controller rebuilds, restore any backups taken (see ). Also, in practice, the nova-compute services on the compute nodes do not always reconnect cleanly to rabbitmq hosted on the controller when it comes back up after a long reboot; a restart on the nova services on the compute nodes is required.

Sometimes a compute node either crashes unexpectedly or requires a reboot for maintenance reasons.

If you need to reboot a compute node due to planned maintenance (such as a software or hardware upgrade), first ensure that all hosted instances have been moved off the node. If your cloud is utilizing shared storage, use the nova live-migration command. First, get a list of instances that need to be moved: compute nodes maintenance maintenance/debugging compute node planned maintenance # nova list --host c01.example.com --all-tenants Next, migrate them one by one: # nova live-migration <uuid> c02.example.com If you are not using shared storage, you can use the --block-migrate option: # nova live-migration --block-migrate <uuid> c02.example.com After you have migrated all instances, ensure that the nova-compute service has stopped: # stop nova-compute If you use a configuration-management system, such as Puppet, that ensures the nova-compute service is always running, you can temporarily move the init files: # mkdir /root/tmp # mv /etc/init/nova-compute.conf /root/tmp # mv /etc/init.d/nova-compute /root/tmp Next, shut down your compute node, perform your maintenance, and turn the node back on. You can reenable the nova-compute service by undoing the previous commands: # mv /root/tmp/nova-compute.conf /etc/init # mv /root/tmp/nova-compute /etc/init.d/ Then start the nova-compute service: # start nova-compute You can now optionally migrate the instances back to their original compute node.

When you reboot a compute node, first verify that it booted successfully. This includes ensuring that the nova-compute service is running: reboot compute node maintenance/debugging compute node reboot # ps aux | grep nova-compute # status nova-compute Also ensure that it has successfully connected to the AMQP server: # grep AMQP /var/log/nova/nova-compute 2013-02-26 09:51:31 12427 INFO nova.openstack.common.rpc.common [-] Connected to AMQP server on 199.116.232.36:5672 After the compute node is successfully running, you must deal with the instances that are hosted on that compute node because none of them are running. Depending on your SLA with your users or customers, you might have to start each instance and ensure that they start correctly.

You can create a list of instances that are hosted on the compute node by performing the following command: instances maintenance/debugging maintenance/debugging instances # nova list --host c01.example.com --all-tenants After you have the list, you can use the nova command to start each instance: # nova reboot <uuid> Any time an instance shuts down unexpectedly, it might have problems on boot. For example, the instance might require an fsck on the root partition. If this happens, the user can use the dashboard VNC console to fix this. If an instance does not boot, meaning virsh list never shows the instance as even attempting to boot, do the following on the compute node: # tail -f /var/log/nova/nova-compute.log Try executing the nova reboot command again. You should see an error message about why the instance was not able to boot In most cases, the error is the result of something in libvirt's XML file (/etc/libvirt/qemu/instance-xxxxxxxx.xml) that no longer exists. You can enforce re-creation of the XML file as well as rebooting the instance by running the following command: # nova reboot --hard <uuid>

In some scenarios, instances are running but are inaccessible through SSH and do not respond to any command. The VNC console could be displaying a boot failure or kernel panic error messages. This could be an indication of file system corruption on the VM itself. If you need to recover files or inspect the content of the instance, qemu-nbd can be used to mount the disk. data inspecting/recovering failed instances If you access or view the user's content and data, get approval first! security issues failed instance data inspection To access the instance's disk (/var/lib/nova/instances/instance-xxxxxx/disk), use the following steps: Suspend the instance using the virsh command. Connect the qemu-nbd device to the disk. Mount the qemu-nbd device. Unmount the device after inspecting. Disconnect the qemu-nbd device. Resume the instance. If you do not follow steps 4 through 6, OpenStack Compute cannot manage the instance any longer. It fails to respond to any command issued by OpenStack Compute, and it is marked as shut down. Once you mount the disk file, you should be able to access it and treat it as a collection of normal directories with files and a directory structure. However, we do not recommend that you edit or touch any files because this could change the access control lists (ACLs) that are used to determine which accounts can perform what operations on files and directories. Changing ACLs can make the instance unbootable if it is not already. access control list (ACL) Suspend the instance using the virsh command, taking note of the internal ID: # virsh list Id Name State ---------------------------------- 1 instance-00000981 running 2 instance-000009f5 running 30 instance-0000274a running # virsh suspend 30 Domain 30 suspended Connect the qemu-nbd device to the disk: # cd /var/lib/nova/instances/instance-0000274a # ls -lh total 33M -rw-rw---- 1 libvirt-qemu kvm 6.3K Oct 15 11:31 console.log -rw-r--r-- 1 libvirt-qemu kvm 33M Oct 15 22:06 disk -rw-r--r-- 1 libvirt-qemu kvm 384K Oct 15 22:06 disk.local -rw-rw-r-- 1 nova nova 1.7K Oct 15 11:30 libvirt.xml # qemu-nbd -c /dev/nbd0 `pwd`/disk Mount the qemu-nbd device. The qemu-nbd device tries to export the instance disk's different partitions as separate devices. For example, if vda is the disk and vda1 is the root partition, qemu-nbd exports the device as /dev/nbd0 and /dev/nbd0p1, respectively: # mount /dev/nbd0p1 /mnt/ You can now access the contents of /mnt, which correspond to the first partition of the instance's disk. To examine the secondary or ephemeral disk, use an alternate mount point if you want both primary and secondary drives mounted at the same time: # umount /mnt # qemu-nbd -c /dev/nbd1 `pwd`/disk.local # mount /dev/nbd1 /mnt/ # ls -lh /mnt/ total 76K lrwxrwxrwx. 1 root root 7 Oct 15 00:44 bin -> usr/bin dr-xr-xr-x. 4 root root 4.0K Oct 15 01:07 boot drwxr-xr-x. 2 root root 4.0K Oct 15 00:42 dev drwxr-xr-x. 70 root root 4.0K Oct 15 11:31 etc drwxr-xr-x. 3 root root 4.0K Oct 15 01:07 home lrwxrwxrwx. 1 root root 7 Oct 15 00:44 lib -> usr/lib lrwxrwxrwx. 1 root root 9 Oct 15 00:44 lib64 -> usr/lib64 drwx------. 2 root root 16K Oct 15 00:42 lost+found drwxr-xr-x. 2 root root 4.0K Feb 3 2012 media drwxr-xr-x. 2 root root 4.0K Feb 3 2012 mnt drwxr-xr-x. 2 root root 4.0K Feb 3 2012 opt drwxr-xr-x. 2 root root 4.0K Oct 15 00:42 proc dr-xr-x---. 3 root root 4.0K Oct 15 21:56 root drwxr-xr-x. 14 root root 4.0K Oct 15 01:07 run lrwxrwxrwx. 1 root root 8 Oct 15 00:44 sbin -> usr/sbin drwxr-xr-x. 2 root root 4.0K Feb 3 2012 srv drwxr-xr-x. 2 root root 4.0K Oct 15 00:42 sys drwxrwxrwt. 9 root root 4.0K Oct 15 16:29 tmp drwxr-xr-x. 13 root root 4.0K Oct 15 00:44 usr drwxr-xr-x. 17 root root 4.0K Oct 15 00:44 var Once you have completed the inspection, unmount the mount point and release the qemu-nbd device: # umount /mnt # qemu-nbd -d /dev/nbd0 /dev/nbd0 disconnected Resume the instance using virsh: # virsh list Id Name State ---------------------------------- 1 instance-00000981 running 2 instance-000009f5 running 30 instance-0000274a paused # virsh resume 30 Domain 30 resumed

If the affected instances also had attached volumes, first generate a list of instance and volume UUIDs: volume maintenance/debugging maintenance/debugging volumes mysql> select nova.instances.uuid as instance_uuid, cinder.volumes.id as volume_uuid, cinder.volumes.status, cinder.volumes.attach_status, cinder.volumes.mountpoint, cinder.volumes.display_name from cinder.volumes inner join nova.instances on cinder.volumes.instance_uuid=nova.instances.uuid where nova.instances.host = 'c01.example.com'; You should see a result similar to the following: +--------------+------------+-------+--------------+-----------+--------------+ |instance_uuid |volume_uuid |status |attach_status |mountpoint | display_name | +--------------+------------+-------+--------------+-----------+--------------+ |9b969a05 |1f0fbf36 |in-use |attached |/dev/vdc | test | +--------------+------------+-------+--------------+-----------+--------------+ 1 row in set (0.00 sec) Next, manually detach and reattach the volumes, where X is the proper mount point: # nova volume-detach <instance_uuid> <volume_uuid> # nova volume-attach <instance_uuid> <volume_uuid> /dev/vdX Be sure that the instance has successfully booted and is at a login screen before doing the above.

Compute nodes can fail the same way a cloud controller can fail. A motherboard failure or some other type of hardware failure can cause an entire compute node to go offline. When this happens, all instances running on that compute node will not be available. Just like with a cloud controller failure, if your infrastructure monitoring does not detect a failed compute node, your users will notify you because of their lost instances. compute nodes failures maintenance/debugging compute node total failures If a compute node fails and won't be fixed for a few hours (or at all), you can relaunch all instances that are hosted on the failed node if you use shared storage for /var/lib/nova/instances. To do this, generate a list of instance UUIDs that are hosted on the failed node by running the following query on the nova database: mysql> select uuid from instances where host = \ 'c01.example.com' and deleted = 0; Next, update the nova database to indicate that all instances that used to be hosted on c01.example.com are now hosted on c02.example.com: mysql> update instances set host = 'c02.example.com' where host = \ 'c01.example.com' and deleted = 0; If you're using the Networking service ML2 plug-in, update the Networking service database to indicate that all ports that used to be hosted on c01.example.com are now hosted on c02.example.com: mysql> update ml2_port_bindings set host = 'c02.example.com' where host = \ 'c01.example.com'; mysql> update ml2_port_binding_levels set host = 'c02.example.com' where host = \ 'c01.example.com'; After that, use the nova command to reboot all instances that were on c01.example.com while regenerating their XML files at the same time: # nova reboot --hard <uuid> Finally, reattach volumes using the same method described in the section Volumes.

It's worth mentioning this directory in the context of failed compute nodes. This directory contains the libvirt KVM file-based disk images for the instances that are hosted on that compute node. If you are not running your cloud in a shared storage environment, this directory is unique across all compute nodes. /var/lib/nova/instances directory maintenance/debugging /var/lib/nova/instances /var/lib/nova/instances contains two types of directories. The first is the _base directory. This contains all the cached base images from glance for each unique image that has been launched on that compute node. Files ending in _20 (or a different number) are the ephemeral base images. The other directories are titled instance-xxxxxxxx. These directories correspond to instances running on that compute node. The files inside are related to one of the files in the _base directory. They're essentially differential-based files containing only the changes made from the original _base directory. All files and directories in /var/lib/nova/instances are uniquely named. The files in _base are uniquely titled for the glance image that they are based on, and the directory names instance-xxxxxxxx are uniquely titled for that particular instance. For example, if you copy all data from /var/lib/nova/instances on one compute node to another, you do not overwrite any files or cause any damage to images that have the same unique name, because they are essentially the same file. Although this method is not documented or supported, you can use it when your compute node is permanently offline but you have instances locally stored on it.

Because of the high redundancy of Object Storage, dealing with object storage node issues is a lot easier than dealing with compute node issues.

If a storage node requires a reboot, simply reboot it. Requests for data hosted on that node are redirected to other copies while the server is rebooting. storage node nodes storage nodes maintenance/debugging storage node reboot

If you need to shut down a storage node for an extended period of time (one or more days), consider removing the node from the storage ring. For example: maintenance/debugging storage node shut down # swift-ring-builder account.builder remove <ip address of storage node> # swift-ring-builder container.builder remove <ip address of storage node> # swift-ring-builder object.builder remove <ip address of storage node> # swift-ring-builder account.builder rebalance # swift-ring-builder container.builder rebalance # swift-ring-builder object.builder rebalance Next, redistribute the ring files to the other nodes: # for i in s01.example.com s02.example.com s03.example.com > do > scp *.ring.gz $i:/etc/swift > done These actions effectively take the storage node out of the storage cluster. When the node is able to rejoin the cluster, just add it back to the ring. The exact syntax you use to add a node to your swift cluster with swift-ring-builder heavily depends on the original options used when you originally created your cluster. Please refer back to those commands.

If a hard drive fails in an Object Storage node, replacing it is relatively easy. This assumes that your Object Storage environment is configured correctly, where the data that is stored on the failed drive is also replicated to other drives in the Object Storage environment. hard drives, replacing maintenance/debugging swift disk replacement This example assumes that /dev/sdb has failed. First, unmount the disk: # umount /dev/sdb Next, physically remove the disk from the server and replace it with a working disk. Ensure that the operating system has recognized the new disk: # dmesg | tail You should see a message about /dev/sdb. Because it is recommended to not use partitions on a swift disk, simply format the disk as a whole: # mkfs.xfs /dev/sdb Finally, mount the disk: # mount -a Swift should notice the new disk and that no data exists. It then begins replicating the data to the disk from the other existing replicas.

A common way of dealing with the recovery from a full system failure, such as a power outage of a data center, is to assign each service a priority, and restore in order. shows an example. service restoration maintenance/debugging complete failures

Example service restoration priority list

Priority	Services
1	Internal network connectivity
2	Backing storage services
3	Public network connectivity for user virtual machines
4	nova-compute, nova-network, cinder hosts
5	User virtual machines
10	Message queue and database services
15	Keystone services
20	cinder-scheduler
21	Image Catalog and Delivery services
22	nova-scheduler services
98	cinder-api
99	nova-api services
100	Dashboard node

Use this example priority list to ensure that user-affected services are restored as soon as possible, but not before a stable environment is in place. Of course, despite being listed as a single-line item, each step requires significant work. For example, just after starting the database, you should check its integrity, or, after starting the nova services, you should verify that the hypervisor matches the database and fix any mismatches.

Maintaining an OpenStack cloud requires that you manage multiple physical servers, and this number might grow over time. Because managing nodes manually is error prone, we strongly recommend that you use a configuration-management tool. These tools automate the process of ensuring that all your nodes are configured properly and encourage you to maintain your configuration information (such as packages and configuration options) in a version-controlled repository. configuration management networks configuration management maintenance/debugging configuration management Several configuration-management tools are available, and this guide does not recommend a specific one. The two most popular ones in the OpenStack community are Puppet, with available OpenStack Puppet modules; and Chef, with available OpenStack Chef recipes. Other newer configuration tools include Juju, Ansible, and Salt; and more mature configuration management tools include CFEngine and Bcfg2.

As for your initial deployment, you should ensure that all hardware is appropriately burned in before adding it to production. Run software that uses the hardware to its limits—maxing out RAM, CPU, disk, and network. Many options are available, and normally double as benchmark software, so you also get a good idea of the performance of your system. hardware maintenance/debugging maintenance/debugging hardware

If you find that you have reached or are reaching the capacity limit of your computing resources, you should plan to add additional compute nodes. Adding more nodes is quite easy. The process for adding compute nodes is the same as when the initial compute nodes were deployed to your cloud: use an automated deployment system to bootstrap the bare-metal server with the operating system and then have a configuration-management system install and configure OpenStack Compute. Once the Compute service has been installed and configured in the same way as the other compute nodes, it automatically attaches itself to the cloud. The cloud controller notices the new node(s) and begins scheduling instances to launch there. cloud controllers new compute nodes and nodes adding compute nodes adding If your OpenStack Block Storage nodes are separate from your compute nodes, the same procedure still applies because the same queuing and polling system is used in both services. We recommend that you use the same hardware for new compute and block storage nodes. At the very least, ensure that the CPUs are similar in the compute nodes to not break live migration.

Adding a new object storage node is different from adding compute or block storage nodes. You still want to initially configure the server by using your automated deployment and configuration-management systems. After that is done, you need to add the local disks of the object storage node into the object storage ring. The exact command to do this is the same command that was used to add the initial disks to the ring. Simply rerun this command on the object storage proxy server for all disks on the new object storage node. Once this has been done, rebalance the ring and copy the resulting ring files to the other storage nodes. Object Storage adding nodes If your new object storage node has a different number of disks than the original nodes have, the command to add the new node is different from the original commands. These parameters vary from environment to environment.

Failures of hardware are common in large-scale deployments such as an infrastructure cloud. Consider your processes and balance time saving against availability. For example, an Object Storage cluster can easily live with dead disks in it for some period of time if it has sufficient capacity. Or, if your compute installation is not full, you could consider live migrating instances off a host with a RAM failure until you have time to deal with the problem.

Almost all OpenStack components have an underlying database to store persistent information. Usually this database is MySQL. Normal MySQL administration is applicable to these databases. OpenStack does not configure the databases out of the ordinary. Basic administration includes performance tweaking, high availability, backup, recovery, and repairing. For more information, see a standard MySQL administration guide. databases maintenance/debugging maintenance/debugging databases You can perform a couple of tricks with the database to either more quickly retrieve information or fix a data inconsistency error—for example, an instance was terminated, but the status was not updated in the database. These tricks are discussed throughout this book.

Review the component's configuration file to see how each OpenStack component accesses its corresponding database. Look for either sql_connection or simply connection. The following command uses grep to display the SQL connection string for nova, glance, cinder, and keystone: # grep -hE "connection ?=" /etc/nova/nova.conf /etc/glance/glance-*.conf /etc/cinder/cinder.conf /etc/keystone/keystone.conf sql_connection = mysql+pymysql://nova:nova@cloud.alberta.sandbox.cybera.ca/nova sql_connection = mysql+pymysql://glance:password@cloud.example.com/glance sql_connection = mysql+pymysql://glance:password@cloud.example.com/glance sql_connection = mysql+pymysql://cinder:password@cloud.example.com/cinder connection = mysql+pymysql://keystone_admin:password@cloud.example.com/keystone The connection strings take this format: mysql+pymysql:// <username> : <password> @ <hostname> / <database name>

As your cloud grows, MySQL is utilized more and more. If you suspect that MySQL might be becoming a bottleneck, you should start researching MySQL optimization. The MySQL manual has an entire section dedicated to this topic: Optimization Overview.

Here's a quick list of various to-do items for each hour, day, week, month, and year. Please note that these tasks are neither required nor definitive but helpful ideas: maintenance/debugging schedule of tasks

Check your monitoring system for alerts and act on them. Check your ticket queue for new tickets.

Check for instances in a failed or weird state and investigate why. Check for security patches and apply them as needed.

Check cloud usage: User quotas Disk space Image usage Large instances Network usage (bandwidth and IP usage) Verify your alert mechanisms are still working.

Check usage and trends over the past month. Check for user accounts that should be removed. Check for operator accounts that should be removed.

Review usage and trends over the past quarter. Prepare any quarterly reports on usage and statistics. Review and plan any necessary cloud additions. Review and plan any major OpenStack upgrades.

Upgrade OpenStack. Clean up after an OpenStack upgrade (any unused or new services to be aware of?).

OpenStack's collection of different components interact with each other strongly. For example, uploading an image requires interaction from nova-api, glance-api, glance-registry, keystone, and potentially swift-proxy. As a result, it is sometimes difficult to determine exactly where problems lie. Assisting in this is the purpose of this section. logging/monitoring tailing logs maintenance/debugging determining component affected

The first place to look is the log file related to the command you are trying to run. For example, if nova list is failing, try tailing a nova log file and running the command again: tailing logs Terminal 1: # tail -f /var/log/nova/nova-api.log Terminal 2: # nova list Look for any errors or traces in the log file. For more information, see . If the error indicates that the problem is with another component, switch to tailing that component's log file. For example, if nova cannot access glance, look at the glance-api log: Terminal 1: # tail -f /var/log/glance/api.log Terminal 2: # nova list Wash, rinse, and repeat until you find the core cause of the problem.

Unfortunately, sometimes the error is not apparent from the log files. In this case, switch tactics and use a different command; maybe run the service directly on the command line. For example, if the glance-api service refuses to start and stay running, try launching the daemon from the command line: daemons running on CLI Command-line interface (CLI) # sudo -u glance -H glance-api This might print the error and cause of the problem. The -H flag is required when running the daemons with sudo because some daemons will write files relative to the user's home directory, and this write may fail if -H is left off. One morning, a compute node failed to run any instances. The log files were a bit vague, claiming that a certain instance was unable to be started. This ended up being a red herring because the instance was simply the first instance in alphabetical order, so it was the first instance that nova-compute would touch. Further troubleshooting showed that libvirt was not running at all. This made more sense. If libvirt wasn't running, then no instance could be virtualized through KVM. Upon trying to start libvirt, it would silently die immediately. The libvirt logs did not explain why. Next, the libvirtd daemon was run on the command line. Finally a helpful error message: it could not connect to d-bus. As ridiculous as it sounds, libvirt, and thus nova-compute, relies on d-bus and somehow d-bus crashed. Simply starting d-bus set the entire chain back on track, and soon everything was back up and running.

When you are getting slow responses from various services, it can be hard to know where to start looking. The first thing to check is the extent of the slowness: is it specific to a single service, or varied among different services? If your problem is isolated to a specific service, it can temporarily be fixed by restarting the service, but that is often only a fix for the symptom and not the actual problem. This is a collection of ideas from experienced operators on common things to look at that may be the cause of slowness. It is not, however, designed to be an exhaustive list.

If OpenStack Identity is responding slowly, it could be due to the token table getting large. This can be fixed by running the keystone-manage token_flush command. Additionally, for Identity-related issues, try the tips in .

OpenStack Image service can be slowed down by things related to the Identity service, but the Image service itself can be slowed down if connectivity to the back-end storage in use is slow or otherwise problematic. For example, your back-end NFS server might have gone down.

OpenStack Block Storage service is similar to the Image service, so start by checking Identity-related services, and the back-end storage. Additionally, both the Block Storage and Image services rely on AMQP and SQL functionality, so consider these when debugging.

Services related to OpenStack Compute are normally fairly fast and rely on a couple of backend services: Identity for authentication and authorization), and AMQP for interoperability. Any slowness related to services is normally related to one of these. Also, as with all other services, SQL is used extensively.

Slowness in the OpenStack Networking service can be caused by services that it relies upon, but it can also be related to either physical or virtual networking. For example: network namespaces that do not exist or are not tied to interfaces correctly; DHCP daemons that have hung or are not running; a cable being physically disconnected; a switch not being configured correctly. When debugging Networking service problems, begin by verifying all physical networking functionality (switch configuration, physical cabling, etc.). After the physical networking is verified, check to be sure all of the Networking services are running (neutron-server, neutron-dhcp-agent, etc.), then check on AMQP and SQL back ends.

Regardless of which AMQP broker you use, such as RabbitMQ, there are common issues which not only slow down operations, but can also cause real problems. Sometimes messages queued for services stay on the queues and are not consumed. This can be due to dead or stagnant services and can be commonly cleared up by either restarting the AMQP-related services or the OpenStack service in question.

Whether you use SQLite or an RDBMS (such as MySQL), SQL interoperability is essential to a functioning OpenStack environment. A large or fragmented SQLite file can cause slowness when using files as a back end. A locked or long-running query can cause delays for most RDBMS services. In this case, do not kill the query immediately, but look into it to see if it is a problem with something that is hung, or something that is just taking a long time to run and needs to finish on its own. The administration of an RDBMS is outside the scope of this document, but it should be noted that a properly functioning RDBMS is essential to most OpenStack services.

While we'd always recommend using your automated deployment system to reinstall systems from scratch, sometimes you do need to remove OpenStack from a system the hard way. Here's how: uninstall operation maintenance/debugging uninstalling Remove all packages. Remove remaining files. Remove databases. These steps depend on your underlying distribution, but in general you should be looking for "purge" commands in your package manager, like aptitude purge ~c $package. Following this, you can look for orphaned files in the directories referenced throughout this guide. To uninstall the database properly, refer to the manual appropriate for the product in use.