事件起因：
在安装ansible过程中，因为系统的yum仓库默认没有ansible的包，所以下载安装了epel源，安装完成后
用yum安装报错如下：
yum install ansible -y
Loaded plugins: priorities, update-motd, upgrade-helper
amzn-main/latest | 2.1 kB 00:00
amzn-updates/latest | 2.3 kB 00:00
epel/x86_64 | 4.3 kB 00:00
Could not retrieve mirrorlist http://apt.sw.be/redhat/el5/en/mirrors-rpmforge error was
14: PYCURL ERROR 22 - "The requested URL returned error: 404 Not Found"
http://apt.sw.be/redhat/el5/en/x86_64/rpmforge/repodata/repomd.xml: [Errno 14] PYCURL ERROR 22 - "The requested URL returned error: 404 Not Found"
Trying other mirror.
One of the configured repositories failed (RHEL latest - RPMforge.net - dag),
and yum doesn't have enough cached data to continue. At this point the only
safe thing yum can do is fail. There are a few ways to work "fix" this:
1. Contact the upstream for the repository and get them to fix the problem.
2. Reconfigure the baseurl/etc. for the repository, to point to a working
upstream. This is most often useful if you are using a newer
distribution release than is supported by the repository (and the
packages for the previous distribution release still work).
3. Disable the repository, so yum won't use it by default. Yum will then
just ignore the repository until you permanently enable it again or use
--enablerepo for temporary usage:
yum-config-manager --disable rpmforge
4. Configure the failing repository to be skipped, if it is unavailable.
Note that yum will try to contact the repo. when it runs most commands,
so will have to try and fail each time (and thus. yum will be be much
slower). If it is a very temporary problem though, this is often a nice
compromise:
yum-config-manager --save --setopt=rpmforge.skip_if_unavailable=true
failure: repodata/repomd.xml from rpmforge: [Errno 256] No more mirrors to try.
解决方法：
执行第三步和第四步中的命令：
yum-config-manager --disable rpmforge
yum-config-manager --save --setopt=rpmforge.skip_if_unavailable=true
然后再重试
yum install ansible -y
安装成功，没有再报错