cloud-init 执行分析
cloud-init主要用于处理instance的初始化配置，如网络、ssh，yum源等。支持多种类型的datasource，如NoCloud, ConfigDrive, OpenNebula, Azure, AltCloud, OVF, MAAS, GCE, OpenStack, CloudSigma, Ec2, CloudStack, SmartOS等，openstack用metadata，config driver配置instance。
执行操作
1.cloud-init提供三个配置Instance的操作命令cloud-init/cloud-module/cloud-single
2.Instance启动时依次执行命令行配置Instance
a. cloud-init init --local
b. cloud-init init
c. cloud-init modules --mode=config
d. cloud-init modules --mode=final
3.文件/etc/cloud/cloud.conf分别配置init,config,final阶段执行操作，如下所示：
1 # The modules that run in the 'init' stage 2 cloud_init_modules: 3 - migrator 4 - seed_random 5 - bootcmd 6 - write-files 7 - growpart 8 - resizefs 9 - set_hostname 10 - update_hostname 11 - update_etc_hosts 12 - ca-certs 13 - rsyslog 14 - users-groups 15 - ssh 16 # The modules that run in the 'config' stage 17 cloud_config_modules: 18 # Emit the cloud config ready event 19 # this can be used by upstart jobs for 'start on cloud-config'. 20 - emit_upstart 21 - disk_setup 22 - mounts 23 - ssh-import-id 24 - locale 25 - set-passwords 26 - grub-dpkg 27 - apt-pipelining 28 - apt-configure 29 - package-update-upgrade-install 30 - landscape 31 - timezone 32 - puppet 33 - chef 34 - salt-minion 35 - mcollective 36 - disable-ec2-metadata 37 - runcmd 38 - byobu 39 # The modules that run in the 'final' stage 40 cloud_final_modules: 41 - rightscale_userdata 42 - scripts-vendor 43 - scripts-per-once 44 - scripts-per-boot 45 - scripts-per-instance 46 - scripts-user 47 - ssh-authkey-fingerprints 48 - keys-to-console 49 - phone-home 50 - final-message 51 - power-state-change
代码
1.根据/etc/cloud/cloud.conf的配置，初始化cloud-init执行环境，如初始化datasource、生成seed /var/lib/cloud。注根据/etc/cloud/cloud.conf指定的datasource_list初始化datasource
2.初始化过程中完成Instance network配置 注 configDriverNet 利用 openstack/content/0000提供的参数，配置各种系统的network，网络配置优先利用openstack/version/network_data.json
3.执行modules对脚本配置Instance，如cc_set_hostname.py
版本
当前社区打包cloud-init的最新版本是0.7.6（2014-10-10），configDrive 利用openstack/content/0000配置网络。
Openstack Mitaka支持利用configDrive的openstack/version/network_data.json，同时支持配置网卡的mtu，建议升级cloud-init到0.7.7
参考文档：
http://cloudinit.readthedocs.io/en/latest/index.html
http://blog.sina.com.cn/s/blog_959491260101m2dd.html
http://cloudinit.readthedocs.io/en/latest/topics/examples.html
