OpenStack和Redis

前言：最近开始捣鼓OpenStack了，在用RDO部署OpenStack的时候，发现装了Redis, 遂决定看看OpenStack哪些地方(可以)用到Redis。

Redis作为OpenStack Dashboard的session storage backend
目前(M版本,后面默认为M版本) OpenStack的Dashboard支持以下三种session storage backend:
Local memory cache
Key-Value store(Memcached, Redis)
Database(Mysql/Mariadb)
其中Local memory cache是最简单而且是最快的，但是缺点也很明显，比如在process和worker之间不能共享，存储随着process结束而结束。Database作为backend相对而言最慢的，但是可以做到scalable,persistent. K-V storage速度上介于两者之间，也可以salable,比较适合小规模部署的环境，一下是配置Redis作为Session storage的backend。
1. 安装依赖包：redis, django-redis。
2. 修改local_settings配置文件:/etc/openstack-dashboard/local_settings.
```
SESSION_ENGINE = 'django.contrib.sessions.backends.cache'

CACHES = {

    "default": {

        "BACKEND": "redis_cache.cache.RedisCache",

        "LOCATION": "127.0.0.1:6379:1",

        "OPTIONS": {

            "CLIENT_CLASS": "redis_cache.client.DefaultClient",

        }

    }

}
```
如果django-redis版本是3.8.0或以上,那么应该要这样配置（https://niwinz.github.io/django-redis/latest/#_configure_as_cache_backend）：
```
SESSION_ENGINE = 'django.contrib.sessions.backends.cache'

CACHES = {

    'default': {

        'BACKEND': 'django_redis.cache.RedisCache',

        'LOCATION': 'redis://127.0.0.1:6379/1',

        'OPTIONS': {

            'CLIENT_CLASS': 'django_redis.client.DefaultClient',

        }

    }

}
```
3. 重启httpd/apache, 登陆Dashboard,然后查看Redis的key:
Redis作为OpenStack Keystone的token storage backend
Keystone支持的Token storage backend目前有三个：
Mysql(Mariadb)
MemCache
Redis

Mysql会有token无限增长的问题，需要定期清理不需要的token, Memcache的问题是空间固定，不好扩容，相对而言Redis是一个不错的选择，一下是配置Redis的步骤：
1. 安装依赖包: Redis.
2. 修改keystone.conf:
```
[cache]

enabled=true

expiration_time=600

backend=dogpile.cache.redis

backend_argument=url:redis://127.0.0.1:6379/2

[token]

caching=true

driver = keystone.token.persistence.backends.kvs.Token  
```

3. 重启keystone(httpd), 查看Redis的key:

OpenStack和Redis-LMLPHP

Redis作为OpenStack Telemetry的多个agent instances之间协作的backend

RDO 安装后，默认的就是Redis作为backend, 参看/etc/ceilometer/ceilometer.conf:

[coordination]

#

# From ceilometer

#

# The backend URL to use for distributed coordination. If left empty, per-

# deployment central agent and per-host compute agent won't do workload

# partitioning and will only function correctly if a single instance of that

# service is running. (string value)

#backend_url = <None>

backend_url = redis://9.114.112.108:6379

# Number of seconds between heartbeats for distributed coordination. (floating

# point value)

#heartbeat = 1.0

# Number of seconds between checks to see if group membership has changed

# (floating point value)

#check_watchers = 10.0