This document discusses running stateful applications in Docker containers. It describes three common approaches: mounting host directories, creating dedicated data volumes, and using Docker volume drivers. It then explains how the Kontena platform automates and simplifies managing stateful services with Docker by automatically creating data volumes and handling data persistence when services are rescheduled. Finally, it provides examples of running MongoDB and MariaDB clusters with stateful persistence using Kontena.

1. Running Docker in Production
Lauri Nevala, Founder
Stateful Services

2. © 2015 Kontena, Inc.

3. Containers Do Not Persist the Data!
© 2015 Kontena, Inc.

4. Apps with Persistent Data
• Databases
• File storages
• Image registries
• Version Control Systems
• etc
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5. © 2015 Kontena, Inc.

6. How to solve the problem
• Mounting a host directory as a data volume
• Creating and mounting a data volume container
• Using Docker volume drivers (>= 1.9)
© 2015 Kontena, Inc.

7. Mounting a host directory as a data
volume
• $ docker run -d -P --name web -v /src/webapp:/opt/webapp
training/webapp python app.py
• Cons:
• Not recommended on production
• Problems with file permissions
• How to keep track what directories are in use?
© 2015 Kontena, Inc.

8. Creating and mounting a data volume
container
• $ docker create -v /dbdata --name dbdata training/postgres /bin/
true
• $ docker run -d --volumes-from dbdata --name db1 training/
postgres
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9. Using Docker volume drivers (>= 1.9)
• $ docker volume create --name my_mongo_volume
• $ docker run -d -v my_mongo_volume:/data –name mongo
mongo:3.0
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10. Stateful Services

11. How?
• Creating services with persistent data with Kontena is easy
© 2015 Kontena, Inc.
# kontena.yml
mysql:
image: mariadb:5.5
stateful: true
$ kontena service create –stateful mongo mongo:3.0

12. Under the Hood
• Kontena creates data volume container for stateful service
instances automatically
• The running container will use volumes from the created data
volume container
• The same data volume container is used for future containers
as well and the data won’t be lost
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13. Some Words of Caution
• Stateful services can not be moved to another node
automatically
• User have to migrate data manually
• Data is not shared between service instances
• Each stateful service instance will have an own data volume container
© 2015 Kontena, Inc.

14. Examples

15. MongoDB cluster – Pure Docker Way
• https://medium.com/@gargar454/deploy-a-mongodb-cluster-in-
steps-9-using-docker-49205e231319#.urb900wm8
• Step 1: Get the IP address of all three servers and export the
following IP addresses variables on all servers by running the
following commands on all servers (replace the IP addresses).
• Ideally you would not have and the IPs can be resolved via DNS. Since
this is a test setup, this is easier.
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root@node*:/# export node1=10.11.32.174
root@node*:/# export node2=10.11.33.37
root@node*:/# export node3=10.11.31.176

16. • Step 2: On node1, start the following mongodb container.
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root@node1:/# docker run --name mongo
-v /home/core/mongo-files/data:/data/db
--hostname="node1.example.com"
-p 27017:27017
-d mongo:2.6.5 –smallfiles
--replSet "rs0"

17. • Step 3: Connect to the replica set and configure it. This is still
on node1. We will start another interactive shell into the mongo
container and start a mongo shell and initiate the replica set.
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root@node1:/# docker exec -it mongo /bin/bash
root@node1:/# mongo
MongoDB shell version: 2.6.5
> rs.initiate()
{
"info2" : "no configuration explicitly specified --
making one",
"me" : "node1.example.com:27017",
"info" : "Config now saved locally. Should come
online in about a minute.",
"ok" : 1
}

18. • Step 4: Start Mongo on the other 2 nodes
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root@node2:/# docker run
--name mongo
-v /home/core/mongo-files/data:/data/db
-v /home/core/mongo-files:/opt/keyfile
--hostname="node2.example.com"
--add-host node1.example.com:${node1}
--add-host node2.example.com:${node2}
--add-host node3.example.com:${node3}
-p 27017:27017 -d mongo:2.6.5
--smallfiles
--replSet "rs0"
root@node3:/# docker run
--name mongo
-v /home/core/mongo-files/data:/data/db
-v /home/core/mongo-files:/opt/keyfile
--hostname="node3.example.com"
--add-host node1.example.com:${node1}
--add-host node2.example.com:${node2}
--add-host node3.example.com:${node3}
-p 27017:27017 -d mongo:2.6.5
--smallfiles
--replSet "rs0"

19. • Step 5: Add the other 2 nodes into the replica set
• Back to node1 where we are in the mongo shell. If you hit enter a few
times here, your prompt should have changed to “rs0:PRIMARY”. This
is because this is the primary node now for replica set “rs0".
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rs0:PRIMARY> rs.add("node2.example.com")
rs0:PRIMARY> rs.add("node3.example.com")

20. Let’s try it out

21. © 2015 Kontena, Inc.

22. MongoDB cluster – The Kontena Way
• Step 1: Create / copy kontena.yml
• https://github.com/kontena/examples/tree/master/mongodb-
cluster
© 2015 Kontena, Inc.

23. © 2015 Kontena, Inc.
peer:
image: mongo:3.0
stateful: true
command: --replSet kontena --smallfiles
instances: 3
hooks:
post_start:
- cmd: sleep 10
name: sleep
instances: 1
oneshot: true
- cmd: mongo --eval "printjson(rs.initiate());"
name: rs_initiate
instances: 1
oneshot: true
- cmd: mongo --eval "printjson(rs.add('%{project}-peer-2'))"
name: rs_add2
instances: 1
oneshot: true
- cmd: mongo --eval "printjson(rs.add('%{project}-peer-3'))"
name: rs_add3
instances: 1
oneshot: true

24. • Step 2: Deploy the stack
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~/mongo-db-cluster$ kontena app deploy

25. MariaDB Galera Cluster
• https://github.com/kontena/examples/tree/master/mariadb-
galera
• Step 1: Write secrets to Kontena Vault
• Step 2: Create / copy kontena.yml
© 2015 Kontena, Inc.
$ kontena vault write GALERA_XTRABACKUP_PASSWORD "top_secret"
$ kontena vault write GALERA_MYSQL_ROOT_PASSWORD "top_secret"

26. © 2015 Kontena, Inc.
seed:
image: jakolehm/galera-mariadb-10.0-xtrabackup:latest
stateful: true
command: seed
secrets:
- secret: GALERA_XTRABACKUP_PASSWORD
name: XTRABACKUP_PASSWORD
type: env
- secret: GALERA_MYSQL_ROOT_PASSWORD
name: MYSQL_ROOT_PASSWORD
type: env
node:
image: jakolehm/galera-mariadb-10.0-xtrabackup:latest
stateful: true
instances: 3
command: "node %{project}-seed.kontena.local,%{project}-node.kontena.local"
secrets:
- secret: GALERA_XTRABACKUP_PASSWORD
name: XTRABACKUP_PASSWORD
type: env
environment:
- KONTENA_LB_MODE=tcp
- KONTENA_LB_BALANCE=leastconn
- KONTENA_LB_INTERNAL_PORT=3306
- KONTENA_LB_EXTERNAL_PORT=3306
links:
- lb
lb:
image: kontena/lb:latest
instances: 2

27. © 2015 Kontena, Inc.
• Step 3: Deploy the stack
• Step 4: Remove seed node
$ kontena app deploy
$ kontena app scale seed 0

28. Thank You!www.kontena.io