前言
一直在思考部署应用到k8s的姿势，之前介绍过helm，个人感觉helm把记录数据放到k8s中不是特别好。最近发现了weave的flux项目(A tool for deploying container images to Kubernetes services)。
flux简介和注意事项
flux简介
先上图，大致看一下flux的理念。
1：flux可以和任意你喜欢的CI工具搭配比如：Drone,CircleCI,gitlabCI等。实际上flux做了CD的环节。
2：flux可以帮助你安全地更新应用。一般会遇到更新过程出错的问题，在flux实现中，每个部署的应用的yaml文件存储在git仓库里，所以每次更改都可以追踪，所以也能精确回滚到任何一个历史版本。这点我是觉得非常好的。当应用需要更新镜像的时候，有以下几个步骤：
- Clone the repository
- Find the deployment files that use the image in question (there may be more than one, since we have e.g., sidecar containers that use the same image)
- Update a few fields in each file, in slightly different ways (e.g., put the image name in the template, and the tag part of the image name in a version label)
- Commit and push the change back to Git
如果只是更新镜像，其实有更简单的操作：
$ fluxctl release --service=sock-shop/front-end --update-all-images
Submitting release job...
Release job submitted, ID cc08f78c-0e66-24a9-9215-82c80cc646c3
Status: Complete.
Here's what happened:
1. Submitted job.
2. Calculating release actions.
3. Release latest images to sock-shop/front-end
4. Clone the config repo.
5. Clone OK.
6. Update 1 images(s) in the resource definition file for sock-shop/front-end: front-end (weaveworksdemos/front-end:0.2.0 -> weaveworksdemos/front-end:7f511af2d21fd601b86b3bed7baa6adfa9c8c669).
7. Update pod controller OK.
8. Commit and push the config repo.
9. Pushed commit: Release latest images to sock-shop/front-end
10. Regrade 1 service(s): sock-shop/front-end.
Took 55.810622454s此处会引出和drone结合的想法。这一点在总结里会详细阐述。
3： flux很好解决了可视化的问题，通过几个指令就能清楚知道正在发生的。flux有controller的概念。
$ fluxctl list-services --namespace=sock-shop
SERVICE CONTAINER IMAGE RELEASE POLICY
sock-shop/cart cart weaveworksdemos/cart:0.3.0
sock-shop/cart-db cart-db mongo
sock-shop/catalogue catalogue weaveworksdemos/catalogue:0.2.0
sock-shop/catalogue-db catalogue-db weaveworksdemos/catalogue-db:0.2.0
sock-shop/front-end front-end weaveworksdemos/front-end:0.2.0
sock-shop/orders orders weaveworksdemos/orders:0.3.0
sock-shop/orders-db orders-db mongo
sock-shop/payment payment weaveworksdemos/payment:0.3.0
sock-shop/queue-master queue-master weaveworksdemos/queue-master:0.3.0
sock-shop/rabbitmq rabbitmq rabbitmq:3
sock-shop/shipping shipping weaveworksdemos/shipping:0.3.0
sock-shop/user user weaveworksdemos/user:0.3.0
sock-shop/user-db user-db weaveworksdemos/user-db:0.3.0
$ fluxctl list-images --service=sock-shop/front-end
SERVICE CONTAINER IMAGE CREATED
sock-shop/front-end front-end weaveworksdemos/front-end
| 7f511af2d21fd601b86b3bed7baa6adfa9c8c669 18 Nov 16 16:00 UTC
| latest 18 Nov 16 16:00 UTC
| snapshot 18 Nov 16 16:00 UTC
| 16007dddd86b2ebb41d8880c53b77580cab13f02 18 Nov 16 11:23 UTC
| a0eaf8c8ffc0b81c2199adaf7d67466891bb3205 17 Nov 16 10:22 UTC
| 1b664cc81d9cf25b213000686a9e8d6477ae1b06 16 Nov 16 20:31 UTC
| ce1efe59c32d3c53344defdda4d5b643272022b8 16 Nov 16 20:29 UTC
| 4c33b216ae902ad89b9c3ca30a99a44833d16d5b 10 Nov 16 21:34 UTC
| 7015587783bc8f7a9c3d5cfa51e5a257fe188c4b 10 Nov 16 11:34 UTC
| 4d3ea2896c81e40a630d36cdc29ce740e7617016 10 Nov 16 11:30 UTC
:
'-> 0.2.0 09 Nov 16 10:26 UTC4：flux实际上可以做到完全自动检测git仓库中yaml文件的变化以及registry中镜像的更新，进而自动部署。
It is most useful when used as a deployment tool at the end of a Continuous Delivery pipeline. Flux will make sure that your new container images and config changes are propagated to the cluster。
大意就是，利用flux作为cd pipeline中最后一个环节，可以很好地解决镜像更新或是yaml文件更新。
flux部署到k8s中注意事项
由于fluxd需要从git仓库中拉取代码，所以会有一个ssh key的问题。
注意flux-secret.yaml文件：
---
apiVersion: v1
kind: Secret
metadata:
name: flux-git-deploy
type: Opaque
并没有data一项。实际上，flux默认会给我们生成一个key。
然后可以执行
$ fluxctl identity
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQC1fndADrb1fp6a+7QusXMU9qI2CNodLyMR82/6Li8rAstUCMRI9SjThAAbzyIfuCX61YCjWGj6qHyPusmfOssErbs7+rs6Q3y0RrACZT7w4HTgODX4aXGMigVY+IztpDv+XYztTqLCwMVfsrQWvo/WrtbltCdjzTP3gR7nWriPzCks3KbEFZkk4bCISJzV19RBCQzJBlE6afOAreCCdhooy80zmWOmHqc+OVDbAVTOC5Bcht/EaHNXGCwcHijiNd0MPah6OKI+gG/eDB2OLixdhoNTzeEYN6vB5Y/wwNuH/m29y46EM6mfXuq6KkD+/YT9J0XiTx就可以获得到public key。这个时候复制到github 仓库的 deploy key即可。
总结
1：如何与drone结合？
首先我是认可将yaml存储在git仓库中，做版本控制。
实际上flux类似于helm，分为fluxd和一个命令行工具fluxctl，fluxd相当于server部署在k8s集群中。那么将fluxctl做成一个drone的插件。放在drone pipeline中最后一步。类似于现在很多helm插件的玩法。
这个插件只需要完成更新镜像的功能即可。毕竟整个pipeline中，更新代码到仓库中触发编译，构建，推送新镜像到harbor，最终对于k8s集群，只需要应用替换新的镜像即可。所以不需要去监听registry这个功能。也不需要关注git中yaml的变化，拉取最新的即可。
具体实现思路：
- 将新的镜像name和要更新的目标，以及yaml文件路径等作为drone插件的输入参数
- 然后执行下面的类似命令
$ fluxctl release --controller=default:deployment/helloworld --update-image=quay.io/weaveworks/helloworld:master-a000001
Submitting release ...
Commit pushed: 33ce4e3
Applied 33ce4e38048f4b787c583e64505485a13c8a7836
CONTROLLER STATUS UPDATES
default:deployment/helloworld success helloworld: quay.io/weaveworks/helloworld:master-9a16ff945b9e -> master-a000001
$ fluxctl list-images --controller default:deployment/helloworld
CONTROLLER CONTAINER IMAGE CREATED
default:deployment/helloworld helloworld quay.io/weaveworks/helloworld
| master-9a16ff945b9e 20 Jul 16 13:19 UTC
| master-b31c617a0fe3 20 Jul 16 13:19 UTC
| master-a000002 12 Jul 16 17:17 UTC
'-> master-a000001 12 Jul 16 17:16 UTC
sidecar quay.io/weaveworks/sidecar
'-> master-a000002 23 Aug 16 10:05 UTC
master-a000001 23 Aug 16 09:53 UTC
2：抛开drone，对于整个paas平台。flux提供的自动监控registry和yaml git 仓库的功能，也能丰富用户的各种玩法。
3：接下来就是drone-flux插件。该插件是我实现本想法而实现的的一个插件。
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