hyper_volume_populate.md

docker volume populate

docker在当一个volume的mountpoint在image里原本有数据的情况下,会把image的数据populate到volume中.这个行为在volume被mount到 多个mountpoint的时候,在不同的docker版本行为有差别.

1. docker 1.10.3,如果volume mount到多个mountpoint,就不会去populate image中原有的数据到volume中

[lear@~]$docker volume create --name foobar
foobar
[lear@~]$docker run --rm -t -v foobar:/vol/data1 -v foobar:/vol/data2 bergwolf/test ls /vol/data1 /vol/data2
/vol/data1:

/vol/data2:

如果volume只mount到一个目录,还是会populate

[lear@~]$docker run --rm -t -v foobar:/vol/data1 bergwolf/test ls /vol/data1
group        hosts        mtab         resolv.conf
hostname     localtime    passwd       shadow

对应的docker代码实现是:

 63 func (daemon *Daemon) populateVolumes(c *container.Container) error {
 64         for _, mnt := range c.MountPoints {
 65                 // skip binds and volumes referenced by other containers (ie, volumes-from)
 66                 if mnt.Driver == "" || mnt.Volume == nil || len(daemon.volumes.Refs(mnt.Volume)) > 1 {
 67                         continue
 68                 }
 69
 70                 logrus.Debugf("copying image data from %s:%s, to %s", c.ID, mnt.Destination, mnt.Name)
 71                 if err := c.CopyImagePathContent(mnt.Volume, mnt.Destination); err != nil {
 72                         return err
 73                 }
 74         }
 75         return nil
 76 }

2. docker 1.11.0, 当一个volume mount到多个mountpoint的时候,先mount那个会populate,后面的mountpoint不会

[hyperpublic@runv]$docker run --rm -t -v foobar:/vol/data1 -v foobar:/vol/data2 voltest ls /vol/data1 /vol/data2
/vol/data1:
group        hosts        mtab         resolv.conf
hostname     localtime    passwd       shadow

/vol/data2:
group        hosts        mtab         resolv.conf
hostname     localtime    passwd       shadow
[hyperpublic@runv]$docker run --rm -t -v foobar2:/vol/data2 -v foobar2:/vol/data1 voltest ls /vol/data1 /vol/data2
/vol/data1:
data2_file

/vol/data2:
data2_file

hyper volume populate

为了简化问题,减少对用户的困扰,hyper的volume会follow docker 1.10.3的行为

1. 当volume mount到一个目录的时候,populate image中的数据到volume中
2. 当volume mount到多个目录的时候,不做populate