RuntimeError: Unable to create a new session key. It is likely that the cache is unavailable.

使用Centos7安装的Mitaka版本，按照官方文档一步步安装Dashboard，输入用户名和密码后出错，如下所示

查看apache日志/var/log/httpd/error_log，发现以下错误

RuntimeError: Unable to create a new session key. It is likely that the cache is unavailable.

解决方法

1.修改配置文件

vim /etc/openstack-dashboard/local_settings

2.将SESSION_ENGINE值修改

原

SESSION_ENGINE = 'django.contrib.sessions.backends.cache'

改为

SESSION_ENGINE = 'django.contrib.sessions.backends.file'

3.重启服务，然后再次登录。

systemctl restart httpd.service memcached.service