I have a Docker image that downloads a large data set, processes it, creating a ton of temporary files in the process and then uploads the final result to S3. I don't need the temp files to be persistent / survive an instance failure, so I want to use instance store for this. For some reason, Docker refuses to use it though.
In my Launch Configuration, I selected an instance type with instance store (c3.8xlarge), then added the two Instance Store volumes as /dev/xvdcz and /dev/sdb.
In the user data, I mount the sdb volume and make it writable:
sudo mkdir /media/storage sudo mount /dev/sdb /media/storage sudo chmod o+rw /media/storage
In the task definition, I create a volume named "InstanceStorage" with the source path "/media/storage" and in the container definition, I added a Mount Point for this volume at /storage.
When I now ssh into the instance while the task is running, and I look at the host's /media/storage directory, it's empty. The task logs clearly show that it can write to the /storage directory of the container. It's just much smaller than the Instance Store - 7.8 GB available instead of 300.
I tried to manually run the Docker container and attach the volume:
docker run -it -v /media/storage:/storage --entrypoint /bin/sh my-docker-image:latest
Same behavior: I can write to /storage, the files even survive exiting and restarting the Docker container, but it's way too small and any files I create in /storage inside the container don't exist in /media/storage on the host.
Looking at df -h at both the host and the container, it becomes clear that it mounted /dev/xvda1 instead -- the volume that also stores the docker images.
Filesystem Size Used Avail Use% Mounted on /dev/xvda1 7,8G 848M 6,9G 11% / devtmpfs 30G 88K 30G 1% /dev tmpfs 30G 0 30G 0% /dev/shm /dev/xvdb 315G 67M 299G 1% /media/storage
Filesystem Size Used Avail Use% Mounted on /dev/mapper/docker-(...) 9.8G 1.1G 8.2G 12% / tmpfs 30G 0 30G 0% /dev tmpfs 30G 0 30G 0% /sys/fs/cgroup /dev/xvda1 7.8G 848M 6.9G 11% /storage shm 64M 0 64M 0% /dev/shm
Why would it do that?