Docker containers slow after restart in Azure VM

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I’m experiencing some weirdness with docker.
I have an Ubuntu server VM running in Windows Azure.
If I start a new docker container for e.g. WordPress like so:

sudo docker run --name some-wordpress --link some-mysql:mysql -p 80:80 -d wordpress

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everything works nicely, I get a resonably snappy site considering the low end VM settings.

However, if I reboot the VM, and start the containers: 

 sudo docker start some-mysql
 sudo docker start some-wordpress

The whole thing runs very slowly, the response time for a single page gets up to some 2-4 seconds.

Removing the containers and starting new ones makes everything run normally again.

What can cause this?

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2 comments

  1. I suspect it has to do with disk usage, does the MySQL container use local disk for storage? When you restart an existing docker container, you reuse the existing volume, normally stored at in a sub folder of /var/lib/docker, whereas a new container creates a new volume.

    I find a few search results saying that Linux on Azure doesn’t handle “soft” reboots well and that stuff doesn’t get reconnected as it should. A “hard” reboot supposedly fixes that.

    Not sure if it helps, my Docker experience is all from AWS.

  2. Your containers are running on a disk which is stored in a blob storage with a max. 500 IOPS per disk. You can avoid hitting the disk (not very realistic with MySQL) or add more disks to use with striping (RAID0) or use SSD (D series in Azure) And depending on your use case, you might also rebase Docker completely to use ephemeral storage (/dev/sdb) – here’s how for CoreOS. BTW, there are some MySQL performance (non-Docker) suggestions in azure.com.