docker update をつかう

$ docker update --restart=always コンテナのID

他にも

Usage:  docker update [OPTIONS] CONTAINER [CONTAINER...]

Update configuration of one or more containers

Options:
      --blkio-weight value          Block IO (relative weight), between 10 and 1000
      --cpu-period int              Limit CPU CFS (Completely Fair Scheduler) period
      --cpu-quota int               Limit CPU CFS (Completely Fair Scheduler) quota
  -c, --cpu-shares int              CPU shares (relative weight)
      --cpuset-cpus string          CPUs in which to allow execution (0-3, 0,1)
      --cpuset-mems string          MEMs in which to allow execution (0-3, 0,1)
      --help                        Print usage
      --kernel-memory string        Kernel memory limit
  -m, --memory string               Memory limit
      --memory-reservation string   Memory soft limit
      --memory-swap string          Swap limit equal to memory plus swap: '-1' to enable unlimited swap
      --restart string              Restart policy to apply when a container exits

メモリや CPU の soft limit など設定できる模様。