Caching layer¶
OpenStack Identity supports a caching layer that is above the
configurable subsystems (for example, token, assignment). OpenStack
Identity uses the
dogpile.cache
library which allows flexible cache back ends. The majority of the
caching configuration options are set in the [cache] section of the
/etc/keystone/keystone.conf file. However, each section that has
the capability to be cached usually has a caching boolean value that
toggles caching.
So to enable only the token back end caching, set the values as follows:
[cache]
enabled=true
[assignment]
caching=false
[token]
caching=true
Note
Since the Juno release, the default setting is enabled for subsystem
caching, but the global toggle is disabled. As a result, no caching
in available unless the global toggle for [cache] is enabled by
setting the value to true.
Caching for tokens and tokens validation¶
The token system has a separate cache_time configuration option,
that can be set to a value above or below the global expiration_time
default, allowing for different caching behavior from the other systems
in OpenStack Identity. This option is set in the [token] section of
the configuration file. Fernet tokens do not need to be persisted in a
back end and therefore must not be cached.
The token revocation list cache time is handled by the configuration
option revocation_cache_time in the [token] section. The
revocation list is refreshed whenever a token is revoked. It typically
sees significantly more requests than specific token retrievals or token
validation calls.
Here is a list of actions that are affected by the cached time: getting a new token, revoking tokens, validating tokens, checking v2 tokens, and checking v3 tokens.
The delete token API calls invalidate the cache for the tokens being acted upon, as well as invalidating the cache for the revoked token list and the validate/check token calls.
Token caching is configurable independently of the revocation_list
caching. Lifted expiration checks from the token drivers to the token
manager. This ensures that cached tokens will still raise a
TokenNotFound flag when expired.
For cache consistency, all token IDs are transformed into the short token hash at the provider and token driver level. Some methods have access to the full ID (PKI Tokens), and some methods do not. Cache invalidation is inconsistent without token ID normalization.
Caching around assignment CRUD¶
The assignment system has a separate cache_time configuration
option, that can be set to a value above or below the global
expiration_time default, allowing for different caching behavior
from the other systems in Identity service. This option is set in the
[assignment] section of the configuration file.
Currently assignment has caching for project, domain, and
role specific requests (primarily around the CRUD actions). Caching
is currently not implemented on grants. The list methods are not
subject to caching.
Here is a list of actions that are affected by the assignment: assign domain API, assign project API, and assign role API.
The create, update, and delete actions for domains, projects and roles will perform proper invalidations of the cached methods listed above.
Note
If a read-only assignment back end is in use, the cache will not
immediately reflect changes on the back end. Any given change may
take up to the cache_time (if set in the [assignment]
section of the configuration file) or the global expiration_time
(set in the [cache] section of the configuration file) before it
is reflected. If this type of delay (when using a read-only
assignment back end) is an issue, it is recommended that caching
be disabled on assignment. To disable caching specifically on
assignment, in the [assignment] section of the configuration
set caching to False.
For more information about the different back ends (and configuration options), see:
dogpile.cache.backends.memcached
Note
The memory back end is not suitable for use in a production environment.
keystone.common.cache.backends.mongo
Configure the Memcached back end example¶
The following example shows how to configure the memcached back end:
[cache]
enabled = true
backend = dogpile.cache.memcached
backend_argument = url:127.0.0.1:11211
You need to specify the URL to reach the memcached instance with the
backend_argument parameter.
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