A Simple Taste Of Docker Swarm
Docker swarm is a native container orchestrator within Docker runtime. It share some common CLI commands with docker. In this artical, let’s take a journey to create a swarm cluster of 3 nodes, then:
- create service to check task schedule;
- scale service to add plasticity to the service;
- service rolling update;
Fasten Seat Belt*, let’s go!!
1.create a swarm on manager node
docker swarm init --advertise-addr 192.168.222.221
the following message will be generated:
docker swarm join --token SWMTKN-1-2qsi0n0s6zz32elnwfbh3invdpguonw3u584z1mqgn601mgpev-30s9ekejekq06tmsjaw6ba5xf 192.168.222.221:2377
if you want to retrive the message again:
docker swarm join-token worker
2.worker node join
ssh login to worker node, execute the docker swarm join command above, then check nodes in mamager node:
docker node ls
ID HOSTNAME STATUS AVAILABILITY MANAGER STATUS ENGINE VERSION
uw8cpilef589arfaap272ewh9 jingle-245 Ready Active 20.10.7
t8or2nv1x8brtuo6oz71k3id4 jingle-246 Ready Active 20.10.7
ca5a7h8zrfme0zrtmy588p2xo * jingle-nas-221 Ready Active Leader 20.10.7
3.drain manager node
docker node update --availability drain jingle-nas-221
ID HOSTNAME STATUS AVAILABILITY MANAGER STATUS ENGINE VERSION
uw8cpilef589arfaap272ewh9 jingle-245 Ready Active 20.10.7
t8or2nv1x8brtuo6oz71k3id4 jingle-246 Ready Active 20.10.7
ca5a7h8zrfme0zrtmy588p2xo * jingle-nas-221 Ready Drain Leader 20.10.7
4.deploy a service to the swarm
docker service create --replicas 2 --name helloworld alpine ping docker.com
output:
sx6ye6p8ldogf8muqy2w579kf
overall progress: 2 out of 2 tasks
1/2: running [==================================================>]
2/2: running [==================================================>]
verify: Service converged
- The docker service create command creates the service.
- The –name flag names the service helloworld.
- The –replicas flag specifies the desired state of 2 running instance.
- The arguments alpine ping docker.com define the service as an Alpine Linux container that executes the command ping docker.com.
check services status:
$docker service ls
ID NAME MODE REPLICAS IMAGE PORTS
sx6ye6p8ldog helloworld replicated 2/2 alpine:latest
5.inspect the service you just created:
docker service inspect --pretty helloworld
ID: sx6ye6p8ldogf8muqy2w579kf
Name: helloworld
Service Mode: Replicated
Replicas: 2
Placement:
UpdateConfig:
Parallelism: 1
On failure: pause
Monitoring Period: 5s
Max failure ratio: 0
Update order: stop-first
RollbackConfig:
Parallelism: 1
On failure: pause
Monitoring Period: 5s
Max failure ratio: 0
Rollback order: stop-first
ContainerSpec:
Image: alpine:latest@sha256:21a3deaa0d32a8057914f36584b5288d2e5ecc984380bc0118285c70fa8c9300
Args: ping docker.com
Init: false
Resources:
Endpoint Mode: vip
you can remove the –pretty, then the messages will be reported in a json format.
Also, you want to know which is your service’s working node:
docker service ps helloworld
ID NAME IMAGE NODE DESIRED STATE CURRENT STATE ERROR PORTS
2wxw6bb34qqw helloworld.1 alpine:latest jingle-246 Running Running 17 minutes ago
mr2ia0snv75a helloworld.2 alpine:latest jingle-245 Running Running 18 minutes ago
6.scale the service in the swarm:
The replicas of the helloworld service is 2. How about scale the replicas to 5? Now, let’s have a try:
sudo docker service scale helloworld=5
helloworld scaled to 5
overall progress: 5 out of 5 tasks
1/5: running [==================================================>]
2/5: running [==================================================>]
3/5: running [==================================================>]
4/5: running [==================================================>]
5/5: running [==================================================>]
verify: Service converged
The message from the command tell us: 5 replias is running… :) Now we do a small check:
sudo docker service ps helloworld
ID NAME IMAGE NODE DESIRED STATE CURRENT STATE ERROR PORTS
2wxw6bb34qqw helloworld.1 alpine:latest jingle-246 Running Running 28 minutes ago
mr2ia0snv75a helloworld.2 alpine:latest jingle-245 Running Running 28 minutes ago
8l2p0bqkklhk helloworld.3 alpine:latest jingle-nas-221 Running Running 2 minutes ago
xev90iwym0h7 helloworld.4 alpine:latest jingle-245 Running Running 2 minutes ago
vtb5advbo1hh helloworld.5 alpine:latest jingle-nas-221 Running Running 2 minutes ago
7.delete the service in the swarm:
sudo docker service rm helloworld
helloworld
Now inspect the helloworld service:
sudo docker service inspect helloworld
[]
Status: Error: no such service: helloworld, Code: 1
8.do rolling updates to a service:
docker service create \
> --replicas 3 \
> --name redis \
> --update-delay 10s \
> redis:3.0.6
rferm7cryv93y6bt01farwtn0
overall progress: 3 out of 3 tasks
1/3: running [==================================================>]
2/3: running [==================================================>]
3/3: running [==================================================>]
verify: Service converged
–update-delay is the time iterval between two task update.
Now, let’s inspect the redis service:
docker service inspect --pretty redis
ID: rferm7cryv93y6bt01farwtn0
Name: redis
Service Mode: Replicated
Replicas: 3
Placement:
UpdateConfig:
Parallelism: 1
Delay: 10s
On failure: pause
Monitoring Period: 5s
Max failure ratio: 0
Update order: stop-first
RollbackConfig:
Parallelism: 1
On failure: pause
Monitoring Period: 5s
Max failure ratio: 0
Rollback order: stop-first
ContainerSpec:
Image: redis:3.0.6@sha256:6a692a76c2081888b589e26e6ec835743119fe453d67ecf03df7de5b73d69842
Init: false
Resources:
Endpoint Mode: vip
We can find three messages here:
- the replcas is 3;
- delay time of UpdateConfig is 10s, and when update failed, the update process will be paused;
- now the image is in 3.0.6 version
Now do a rolling update to v3.0.7:
docker service update --image redis:3.0.7 redis
redis
overall progress: 3 out of 3 tasks
1/3: running [==================================================>]
2/3: running [==================================================>]
3/3: running [==================================================>]
verify: Service converged
check the service again:
docker service inspect --pretty redis
ID: rferm7cryv93y6bt01farwtn0
Name: redis
Service Mode: Replicated
Replicas: 3
UpdateStatus:
State: completed
Started: 6 minutes ago
Completed: 2 minutes ago
Message: update completed
Placement:
UpdateConfig:
Parallelism: 1
Delay: 10s
On failure: pause
Monitoring Period: 5s
Max failure ratio: 0
Update order: stop-first
RollbackConfig:
Parallelism: 1
On failure: pause
Monitoring Period: 5s
Max failure ratio: 0
Rollback order: stop-first
ContainerSpec:
Image: redis:3.0.7@sha256:730b765df9fe96af414da64a2b67f3a5f70b8fd13a31e5096fee4807ed802e20
Init: false
Resources:
Endpoint Mode: vip
Ha！Look at the UpdateStatus, they tell the update result!
Use service ps get the update trace:
sudo docker service ps redis
ID NAME IMAGE NODE DESIRED STATE CURRENT STATE ERROR PORTS
mwf4b47w6lgm redis.1 redis:3.0.7 jingle-245 Running Running 5 minutes ago
xh6j6yd2blsu \_ redis.1 redis:3.0.6 jingle-245 Shutdown Shutdown 5 minutes ago
wcv1n4d5trgk redis.2 redis:3.0.7 jingle-246 Running Running 5 minutes ago
skb5fstmv1x5 \_ redis.2 redis:3.0.6 jingle-246 Shutdown Shutdown 7 minutes ago
jmfhokb3rbpl redis.3 redis:3.0.7 jingle-nas-221 Running Running 8 minutes ago
ru8ehvz3uzeb \_ redis.3 redis:3.0.6 jingle-nas-221 Shutdown Shutdown 8 minutes ago