External-Mirrors/awx
2
0
Fork 0
mirror of https://github.com/ansible/awx.git synced 2026-02-01 01:28:09 -03:30
Code Issues Packages Projects Releases Wiki Activity

replace our memcached-based fact cache implementation with local files

Browse Source 
see: https://github.com/ansible/ansible-tower/issues/7840
This commit is contained in:
Ryan Petrello
2018-01-12 17:27:54 -05:00
parent e0c04df1ee
commit 983b192a45
6 changed files with 198 additions and 336 deletions
Download Patch File Download Diff File Expand all files Collapse all files

45
docs/fact_cache.md
View File

@@ -1,21 +1,40 @@
# Tower as an Ansible Fact Cache
Tower can store and retrieve per-host facts via an Ansible Fact Cache Plugin. This behavior is configurable on a per-job-template basis. When enabled, Tower will serve fact requests for all Hosts in an Inventory related to the Job running. This allows users to use Job Templates with `--limit` while still having access to the entire Inventory of Host facts. The Tower Ansible Fact Cache supports a global timeout settings that it enforces per-host. The setting is available in the CTiT interface under the Jobs category with the name `ANSIBLE_FACT_CACHE_TIMEOUT` and is in seconds.
# AWX as an Ansible Fact Cache
AWX can store and retrieve per-host facts via an Ansible Fact Cache Plugin.
This behavior is configurable on a per-job-template basis. When enabled, AWX
will serve fact requests for all Hosts in an Inventory related to the Job
running. This allows users to use Job Templates with `--limit` while still
having access to the entire Inventory of Host facts.
## Tower Fact Cache Implementation Details
### Tower Injection
In order to understand the behavior of Tower as a fact cache you will need to understand how fact caching is achieved in Tower. Upon a Job invocation with `use_fact_cache=True`, Tower will inject, into memcached, all `ansible_facts` associated with each Host in the Inventory associated with the Job. Jobs invoked with `use_fact_cache=False` will not inject `ansible_facts` into memcached. The cache key is of the form `inventory_id-host_name` so that hosts with the same name in different inventories do not clash. A list of all hosts in the inventory is also injected into memcached with key `inventory_id` and value `[host_name1, host_name2, ..., host_name3]`.
## AWX Fact Cache Implementation Details
### AWX Injection
In order to understand the behavior of AWX as a fact cache you will need to
understand how fact caching is achieved in AWX. When a Job launches with
`use_fact_cache=True`, AWX will write all `ansible_facts` associated with
each Host in the associated Inventory as JSON files on the local file system
(one JSON file per host). Jobs invoked with `use_fact_cache=False` will not
write `ansible_facts` files.
### Ansible plugin usage
The Ansible fact cache plugin that ships with Tower will only be enabled on Jobs that have fact cache enabled, `use_fact_cache=True`. The fact cache plugin running in Ansible will connect to the same memcached instance. A `get()` call to the fact cache interface in Ansible will result in a looked into memcached for the host-specific set of facts. A `set()` call to the fact cache will result in an update to memcached record along with the modified time.
When `use_fact_cache=True`, Ansible will be configured to use the `jsonfile`
cache plugin. Any `get()` call to the fact cache interface in Ansible will
result in a JSON file lookup for the host-specific set of facts. Any `set()`
call to the fact cache will result in a JSON file being written to the local
file system.
### Tower Cache to DB
When a Job finishes running that has `use_fact_cache=True` enabled, Tower will go through memcached and get all records for the hosts in the Inventory. Any records with update times newer than the database per-host `ansible_facts_modified` value will result in the `ansible_facts`, `ansible_facts_modified` from memcached being saved to the database. Note that the last value of the Ansible fact cache is retained in `ansible_facts`. The globla timeout and/or individual job template `use_fact_cache` setting will not clear the per-host `ansible_facts`.
### AWX Cache to DB
When a Job with `use_fact_cache=True` finishes running, AWX will look at all
of the local JSON files that represent the fact data. Any records with file
modification times that have increased (because Ansible updated the file via
`cache.set()`) will result in the latest value being saved to the database. On
subsequent playbook runs, AWX will _only_ inject cached facts that are _newer_
than `settings.ANSIBLE_FACT_CACHE_TIMEOUT` seconds.
### Caching Behavior
Tower will always inject the host `ansible_facts` into memcached. The Ansible Tower Fact Cache Plugin will choose to present the cached values to the user or not based on the per-host `ansible_facts_modified` time and the global `ANSIBLE_FACT_CACHE_TIMEOUT`.
## Tower Fact Logging
New and changed facts will be logged via Tower's logging facility. Specifically, to the `system_tracking` namespace or logger. The logging payload will include the fields: `host_name`, `inventory_id`, and `ansible_facts`. Where `ansible_facts` is a dictionary of all ansible facts for `host_name` in Tower Inventory `inventory_id`.
## AWX Fact Logging
New and changed facts will be logged via AWX's logging facility. Specifically,
to the `system_tracking` namespace or logger. The logging payload will include
the fields: `host_name`, `inventory_id`, and `ansible_facts`. Where
`ansible_facts` is a dictionary of all ansible facts for `host_name` in AWX
Inventory `inventory_id`.
## Integration Testing
* ensure `clear_facts` set's `hosts/<id>/ansible_facts` to `{}`