Docker Storage

Daniel Lauzon

2017-01-25

Outline

• The context
  • scaling containers - stateless vs stateful
  • State of volume drivers
• The challenge
  • Managing containers requiring persistence
• The how
• • Demo!

scaling - stateless

solved

Volume drivers

• local driver

docker run -it --rm -v $(pwd)/data:/data ubuntu

What if we are on a swarm?

• Host-local data might be fine
• What about databases?

State of volume drivers

• Flocker
• Infinit.sh
• RexRay (EMC)
• Convoy (Rancher)
• Kubernetes...
• Old list here

The challenge

• Managing persistence (databases)
• Adapted to containers
• Works with multiple hosts

• Store in Volumes
• Need Volumes to follow containers
• Volume lifecycle: provision,delete,...

Resiliency

• Tolerance to Failure
• Disaster recovery

Performance

• Sharding
• Dynamic rebalancing
• Auto Scaling...

The How

• Volume drivers
• batteries (not quite) included

These are the two solutions I got to work:

• RexRay (libStorage)
• Kubernetes Persistent Volume claims

RexRay - Swarm

• docker-machine create, ...
• docker swarm init, join,join,join
• install extra software on host

docker volume create -d rexray --name myvolume --opt=size=10

docker volume create -d rexray --name myvolume --opt=size=10 \
  --opt=type=gp2

docker volume create -d rexray --name myvolume --opt=size=10 \
  --opt=type=io1 --opt=iops=150

RexRay - Swarm

# -- create a volume
docker volume create -d rexray --name myvolume --opt=size=10

# -- run and attach from host 1
eval $(docker-machine env node1)
docker run --rm -it --name ubu -v myvolume:/mypath ubuntu
.. do things on myvolume

# -- run and attach from host 2

eval $(docker-machine env node2)
docker run --rm -it --name ubu -v myvolume:/mypath ubuntu

.. do things on myvolume

RexRay - Swarm

# -- create a volume
docker volume create -d rexray --name myvolume --opt=size=10

# -- service runs container on random host
# --  disk follows container
docker service create --name ubu \
 --mount type=volume,source=myvolume,target=/mypath \
 ubuntu bash -c log-a-message

log-a-message == 
for i in $(seq 1 10); do \ 
  echo $(date -Iseconds) host:$(hostname) Message $i>>/mypath/mylog.txt; 
  sleep 1; 
done

Kubernetes - PVC

Examples of databases which scale horizontally:

• use kops to provision (aws)
• ebs driver included
• Stateful Set
• Persistent Volume Claims

• CockroachDB
• CrateDB

Kubernetes - PVC

kubectl create -f cockroachdb-statefulset.yaml

CockroachDB

• PostreSQL line compatible

volumeClaimTemplates:
  - metadata:
      name: datadir
      annotations:
        volume.alpha.kubernetes.io/storage-class: anything
    spec:
      accessModes:
        - "ReadWriteOnce"
      resources:
        requests:
          storage: 1Gi

Kubernetes - PVC

kubectl run -it --rm generator ...

• run small load
• scale up database nodes
• kill a node
• generator runs uninterrupted

kubectl scale statefulset cockroachdb --replicas=3

kubectl delete pod cockroachdb-1

Takeaways

Managed Persistence - Volume Drivers

• Maturing quickly
• Declarative/Scalable Databases coming!
• Buyer beware

Thanks

Daniel Lauzon

@daneroo