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 service 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 SQL back end.
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.