Orchestration: Docker

Question 1

How to initialise a new swarm?

Answer 1

On the swarm manager:

docker swarm init –advertise-addr

Question 2

How to get the join token for the swarm?

Answer 2

docker swarm join-token worker/manager

Question 3

How to rotate the join token and generate a new one?

Answer 3

docker swarm join-token –rotate worker

Question 4

How to create a docker service with 3 replicas?

Answer 4

docker service create –name my_service –replicas 3 ubuntu

Question 5

How to increase the number of replicas for a running service?

Answer 5

1. docker service scale my_service=5 my_other_service=5

2. docker service update –replicas=5 my_service

Question 6

Replicated vs Global docker services?

Answer 6

Replicated sets how many replicas you want

Global sets exactly one replica per node, and automatically added to new nodes

Question 7

How to specify whether a service is replicated or global?

Answer 7

Replicated is default, but:

docker service create –name my_service –mode global ubuntu

Question 8

How to drain a swarm node?

Answer 8

docker node update –availability drain node_name

Question 9

How to test a docker-compose file?

Answer 9

docker-compose config

Question 10

Syntax to deploy a basic docker stack?

Answer 10

docker stack deploy –compose-file stack_name

Question 11

How to lock a docker swarm?

Answer 11

docker swarm update –autolock=true

Question 12

How to unlock a docker swarm?

Answer 12

docker swarm unlock

and use the unlock key provided when locking

Question 13

How to find the key of an unlocked cluster?

Answer 13

docker swarm unlock-key

Question 14

3 possible reasons why a swarm service will be in the pending state?

Answer 14

1. All nodes are drained (no available nodes)
2. There is no node with the service requested memory available
3. Placement preferences are not able to be met

Question 15

How to view the reason why a service task is in the pending state?

Answer 15

docker service inspect task_name

Question 16

Placement preferences vs Placement constraints?

Answer 16

Prefs allow you to spread over a specific tag

Constraints limit where services can be run

Question 17

4 ways to control placement of services across nodes?

Answer 17

1. Replicated or Global mode
2. Resource constraints (CPU/Mem/etc)
3. Placement constraints
4. Placement preferences

Question 18

How can templates be used for values when creating a docker service?

Answer 18

docker service create –name my_service –hostname=”{{.Node.Hostname}}-{{.Service.Name}}” nginx

Question 19

Which flags support the use of templated values?

Answer 19

• -env
• -hostname
• -mount

Question 20

How to prevent the manager node from accepting tasks?

Answer 20

Drain the manager node:

docker node update –availability drain manager_node

Question 21

How to recover from losing a quorum on swarm?

Answer 21

From a manager node run:

docker swarm init –force-new-cluster –advertise-addre node_ip:node_port

Question 22

What are the 4 docker system child commands?

Answer 22

docker system info
docker system df
docker system events
docker system prune