【原创】大叔经验分享（81）marathon上app无法重启

通过api调用marathon重启app后出现deployment，但是app不会重启，配置如下：

  "constraints": [
    [
      "hostname",
      "UNIQUE"
    ],
    [
      "hostname",
      "LIKE",
      "HOST-00[12]"
    ]
  ]

指定app只能在2个服务器上启动，并且每个服务器只能启动1个instance，

解决方法如下：

  "upgradeStrategy": {
    "maximumOverCapacity": 1,
    "minimumHealthCapacity": 0.5
  }

官方解释如下：

Marathon allows you to perform rolling restarts to deploy new versions of applications. In general, there are two phases to deploying a new version of an application: starting a set of processes with the new version and stopping the set of processes with the old version.

In Marathon, you can perform a rolling restart by defining an upgrade strategy with a minimumHealthCapacity at the application level.

The minimumHealthCapacity is a percentage which, when applied to the instance count, defines the number of healthy instances that a certain version of the application must have at all times during update. Number of healthy instances is rounded up (ceil).

• minimumHealthCapacity == 0 : All old instances can be killed before the new version is deployed.
• minimumHealthCapacity == 1 : All instances of the new version are deployed side by side before the old version is stopped.
• minimumHealthCapacity between 0 and 1 : Scale the old version to minimumHealthCapacity and start the new version to minimumHealthCapacity side by side. If this is completed successfully, the new version is scaled to 100% and the old version is stopped. Number of healthy instances is rounded up (ceil). E.g. 3 instances and minimumHealthCapacity 0.7 gives us ⌈3 × 0.7⌉ = ⌈2.1⌉ = 3 so all instances will remain.

问题原因：minimumHealthCapacity默认为1，即只有新实例启动之后才会停止老实例，这与hostname:UNIQUE冲突了；

参考：

marathon constraints

https://mesosphere.github.io/marathon/docs/constraints.html

marathon app deployment

http://mesosphere.github.io/marathon/docs/deployments.html