OpenStack和Redis

前言： 最近開始搗鼓OpenStack了，在用RDO部署OpenStack的時候，發現裝了Redis, 遂決定看看OpenStack哪些地方(能夠)用到Redis。

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•  Redis做爲OpenStack Dashboard的session storage backend
  目前(M版本,後面默認爲M版本) OpenStack的Dashboard支持如下三種session storage backend:
  Local memory cache
  Key-Value store(Memcached, Redis)
  Database(Mysql/Mariadb)
  其中Local memory cache是最簡單並且是最快的，可是缺點也很明顯，好比在process和worker之間不能共享，存儲隨着process結束而結束。Database做爲backend相對而言最慢的，可是能夠作到scalable,persistent. K-V storage速度上介於二者之間，也能夠salable,比較適合小規模部署的環境，一下是配置Redis做爲Session storage的backend。
  
  1. 安裝依賴包：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",
          }
      }
  }

  若是django-redis版本是3.8.0或以上,那麼應該要這樣配置（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. 重啓httpd/apache, 登錄Dashboard,而後查看Redis的key:
  

   

•  Redis做爲OpenStack Keystone的token storage backend
  Keystone支持的Token storage backend目前有三個：
  Mysql(Mariadb)
  MemCache
  Redis
  
  Mysql會有token無限增加的問題，須要按期清理不須要的token, Memcache的問題是空間固定，很差擴容，相對而言Redis是一個不錯的選擇，一下是配置Redis的步驟：
  1. 安裝依賴包: 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. 重啓keystone(httpd), 查看Redis的key:

       

 

• Redis做爲OpenStack Telemetry的多個agent instances之間協做的backend

       RDO 安裝後，默認的就是Redis做爲backend, 參看/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