21 Days of Docker-Day 14 -Introduction to Docker Swarm- Part 1

  • To see more info about Swarm
 $ docker info
 Client:
  Debug Mode: false
 Server:
  Containers: 0
   Running: 0
   Paused: 0
   Stopped: 0
  Images: 0
  Server Version: 19.03.4
  Storage Driver: devicemapper
   Pool Name: docker-259:1-67129954-pool
   Pool Blocksize: 65.54kB
   Base Device Size: 10.74GB
   Backing Filesystem: xfs
   Udev Sync Supported: true
   Data file: /dev/loop0
   Metadata file: /dev/loop1
   Data loop file: /var/lib/docker/devicemapper/devicemapper/data
   Metadata loop file: /var/lib/docker/devicemapper/devicemapper/metadata
   Data Space Used: 11.73MB
   Data Space Total: 107.4GB
   Data Space Available: 13.43GB
   Metadata Space Used: 17.36MB
   Metadata Space Total: 2.147GB
   Metadata Space Available: 2.13GB
   Thin Pool Minimum Free Space: 10.74GB
   Deferred Removal Enabled: true
   Deferred Deletion Enabled: true
   Deferred Deleted Device Count: 0
   Library Version: 1.02.158-RHEL7 (2019-05-13)
  Logging Driver: json-file
  Cgroup Driver: cgroupfs
  Plugins:
   Volume: local
   Network: bridge host ipvlan macvlan null overlay
   Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
  Swarm: active
   NodeID: w45sgx9gjpijtrq445avrd9wt
   Is Manager: true
   ClusterID: xz9d4b2z4we24wcg7j0e7zng4
   Managers: 1
   Nodes: 3
   Default Address Pool: 10.0.0.0/8  
   SubnetSize: 24
   Data Path Port: 4789
   Orchestration:
    Task History Retention Limit: 5
   Raft:
    Snapshot Interval: 10000
    Number of Old Snapshots to Retain: 0
    Heartbeat Tick: 1
    Election Tick: 10
   Dispatcher:
    Heartbeat Period: 5 seconds
   CA Configuration:
    Expiry Duration: 3 months
    Force Rotate: 0
   Autolock Managers: false
   Root Rotation In Progress: false
   Node Address: 172.31.21.46
   Manager Addresses:
    172.31.21.46:2377
  Runtimes: runc
  Default Runtime: runc
  Init Binary: docker-init
  containerd version: b34a5c8af56e510852c35414db4c1f4fa6172339
  runc version: 3e425f80a8c931f88e6d94a8c831b9d5aa481657
  init version: fec3683
  Security Options:
   seccomp
    Profile: default
  Kernel Version: 3.10.0-1062.1.2.el7.x86_64
  Operating System: CentOS Linux 7 (Core)
  OSType: linux
  Architecture: x86_64
  CPUs: 2
  Total Memory: 1.758GiB
  Name: plakhera12c.mylabserver.com
  ID: F4RB:NVBA:5ABO:CRPA:K3HA:DPAG:RHX5:KXRK:NXP2:JNIG:YM46:QOYP
  Docker Root Dir: /var/lib/docker
  Debug Mode: false
  Registry: https://index.docker.io/v1/
  Labels:
  Experimental: false
  Insecure Registries:
   127.0.0.0/8
  Live Restore Enabled: false 

Service

  • To deploy an application image when Docker Engine is in swarm mode, you create a service.
  • When you deploy the service to the swarm, the swarm manager accepts your service definition as the desired state for the service. Then it schedules the service on nodes in the swarm as one or more replica tasks. The tasks run independently of each other on nodes in the swarm.
$ docker service create --name mytestswarmserver --replicas 1 nginx
wgsg0ehf45kxe6fzit4nt50ey
overall progress: 0 out of 1 tasks 
overall progress: 0 out of 1 tasks 
overall progress: 1 out of 1 tasks 
1/1: running   [==================================================>] 
  • The docker service create command creates the service.
  • The --name flag names the service mytestswarmserver.
  • The --replicas flag specifies the desired state of 1 running instance.
  • The arguments nginx  define the service as an nginx Linux container

Run docker service ls to see the list of running services:

$ docker service ls 
ID                  NAME                MODE                REPLICAS            IMAGE               PORTS
wgsg0ehf45kx        mytestswarmserver   replicated          1/1                 nginx:latest        

The following command shows all the tasks that are part of the mytestswarmserver service:

$ docker service ps mytestswarmserver
ID                  NAME                  IMAGE               NODE                          DESIRED STATE       CURRENT STATE            ERROR               PORTS
0q0a4qt7p76q        mytestswarmserver.1   nginx:latest        plakhera12c.mylabserver.com   Running             Running 10 minutes ago 
  • As you can see that currently, service is running on plakhera12c.mylabserver.com
  • You can also verify that nginx container is up and running on plakhera12c.mylabserver.com by using
$ docker container ls
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS               NAMES
208d1a371e9a        nginx:latest        "nginx -g 'daemon of…"   15 minutes ago      Up 15 minutes       80/tcp              mytestswarmserver.1.0q0a4qt7p76q38sew5u8thiuy
  • Let’s do some experiment, let stop the nginx container on plakhera12 machine
$ docker stop 208d1a371e9a
208d1a371e9a
  • Let see the swarm magic here, it automatically brings up the service on plakhera13c.mylabserver.com
$ docker service ps wgsg0ehf45kx
ID                  NAME                      IMAGE               NODE                          DESIRED STATE       CURRENT STATE                 ERROR               PORTS
pivgm8nsupi6        mytestswarmserver.1       nginx:latest        plakhera13c.mylabserver.com   Ready               Preparing 2 seconds ago                           
k95zl8mmb5c1         \_ mytestswarmserver.1   nginx:latest             plakhera12c.mylabserver.com   Shutdown            Complete about a minute ago                       
  • Some more testing, let login to plakhera13c.mylabserver.com and shutdown docker daemon itself
$ sudo systemctl stop docker
  • Ready for one more swarm magic, it again brings up the service on plakhera12c.mylabserver.com without your intervention
$ docker service ps wgsg0ehf45kx
ID                  NAME                      IMAGE               NODE                          DESIRED STATE       CURRENT STATE            ERROR               PORTS
o5f7vz5e9bjx        mytestswarmserver.1       nginx:latest        plakhera12c.mylabserver.com   Running             Running 4 seconds ago                        
pivgm8nsupi6         \_ mytestswarmserver.1   nginx:latest        plakhera13c.mylabserver.com   Shutdown            Running 23 seconds ago                       
k95zl8mmb5c1         \_ mytestswarmserver.1   nginx:latest              plakhera12c.mylabserver.com   Shutdown            Complete 5 minutes ago 
  • Scaling Swarm Service: The scale command enables you to scale one or more replicated services either up or down to the desired number of replicas
$ docker service scale mytestswarmserver=5 
mytestswarmserver 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 
  • If you again check the list of tasks for that particular service
$ docker service ps mytestswarmserver
ID                  NAME                      IMAGE               NODE                          DESIRED STATE       CURRENT STATE           ERROR               PORTS
o5f7vz5e9bjx        mytestswarmserver.1       nginx:latest        plakhera12c.mylabserver.com   Running             Running 2 hours ago                               plakhera14c.mylabserver.com   Running             Running 2 minutes ago                       
9hond3nsebry        mytestswarmserver.3       nginx:latest        plakhera14c.mylabserver.com   Running             Running 2 minutes ago                       
q27r94oby3mb        mytestswarmserver.4       nginx:latest        plakhera12c.mylabserver.com   Running             Running 2 minutes ago                       
36wwuepguejo        mytestswarmserver.5       nginx:latest        plakhera14c.mylabserver.com   Running             Running 2 minutes ago                       
  • The same way we scale up service, we can scale it down
$ docker service scale mytestswarmserver=3 
mytestswarmserver scaled to 3
overall progress: 3 out of 3 tasks 
1/3: running   [==================================================>] 
2/3: running   [==================================================>] 
3/3: running   [==================================================>] 
verify: Service converged 
  • Similar to scale, we have update command
$ docker service update --replicas 4 mytestswarmserver 
mytestswarmserver
overall progress: 4 out of 4 tasks 
1/4: running   [==================================================>] 
2/4: running   [==================================================>] 
3/4: running   [==================================================>] 
4/4: running   [==================================================>] 
verify: Service converged 
  • But there is one subtle difference between scale and update
  • To understand that, let’s create one more service
$ docker service create --name mytestswarmserver01 --replicas 2 nginx
x6wdo9c8nzi42xr58bqd9ma7o
overall progress: 2 out of 2 tasks 
1/2: running   [==================================================>] 
2/2: running   [==================================================>] 
verify: Service converged 
  • Using Docker service create you can scale multiple services
$ docker service scale mytestswarmserver=5  mytestswarmserver01=3
mytestswarmserver scaled to 5
mytestswarmserver01 scaled to 3
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 
overall progress: 3 out of 3 tasks 
1/3: running   [==================================================>] 
2/3: running   [==================================================>] 
3/3: running   [==================================================>] 
verify: Service converged 
  • But using update you can only scale one service at a time
$ docker service update --replicas 6 mytestswarmserver mytestswarmserver01
"docker service update" requires exactly 1 argument.
See 'docker service update --help'.

Usage:  docker service update [OPTIONS] SERVICE

Update a service

Replicated Services/Global Services

So far, in the replicated services model, the swarm manager distributes a specific number of replica tasks among the nodes based upon the scale you set in the desired state.

For global services, the swarm runs one task for the service on every available node in the cluster. Let say we have monitoring service whose daemon needs to be installed in each swarm node

$ docker service create --name myglobal --mode global nginx
juqr8xuetjh12wfbhytbcu4ds
overall progress: 3 out of 3 tasks 
x1v3x9ejsnpz: running   [==================================================>] 
w45sgx9gjpij: running   [==================================================>] 
b5lyurguajin: running   [==================================================>] 
verify: Service converged 
  • To verify it
$ docker service ps myglobal
ID                  NAME                                 IMAGE               NODE                          DESIRED STATE       CURRENT STATE           ERROR               PORTS
d3mr45xdeqen        myglobal.x1v3x9ejsnpzgateb9xhbi431   nginx:latest        plakhera14c.mylabserver.com   Running             Running 3 minutes ago                       
jzk96ycyp2fd        myglobal.w45sgx9gjpijtrq445avrd9wt   nginx:latest        plakhera12c.mylabserver.com   Running             Running 3 minutes ago                       
y1p3lri0h1w0        myglobal.b5lyurguajincw1l9see0etr7   nginx:latest        plakhera13c.mylabserver.com   Running             Running 3 minutes ago                      
  • Draining Swarm Node
  • Sometimes, such as planned maintenance times, you need to set a node to DRAIN availability. DRAIN availability prevents a node from receiving new tasks from the swarm manager. It also means the manager stops tasks running on the node and launches replica tasks on a node with ACTIVE availability.
$ docker node update --availability drain plakhera14c.mylabserver.com
plakhera14c.mylabserver.com
  • To check the status
$ docker node ls
ID                            HOSTNAME                      STATUS              AVAILABILITY        MANAGER STATUS      ENGINE VERSION
w45sgx9gjpijtrq445avrd9wt *   plakhera12c.mylabserver.com   Ready               Active              Leader              19.03.4
b5lyurguajincw1l9see0etr7     plakhera13c.mylabserver.com   Ready               Active                                  19.03.4
x1v3x9ejsnpzgateb9xhbi431     plakhera14c.mylabserver.com   Ready               Drain  <---                                 19.03.4
  • To put the node back in active state
$ docker node update --availability active plakhera14c.mylabserver.com
plakhera14c.mylabserver.com
  • To check the status
$ docker node ls
ID                            HOSTNAME                      STATUS              AVAILABILITY        MANAGER STATUS      ENGINE VERSION
w45sgx9gjpijtrq445avrd9wt *   plakhera12c.mylabserver.com   Ready               Active              Leader              19.03.4
b5lyurguajincw1l9see0etr7     plakhera13c.mylabserver.com   Ready               Active                                  19.03.4
x1v3x9ejsnpzgateb9xhbi431     plakhera14c.mylabserver.com   Ready               Active                                  19.03.4

Display detailed information on one or more services

$ docker service inspect mytestswarmserver01 --pretty

ID:		x6wdo9c8nzi42xr58bqd9ma7o
Name:		mytestswarmserver01
Service Mode:	Replicated
 Replicas:	3
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:		nginx:[email protected]:77ebc94e0cec30b20f9056bac1066b09fbdc049401b71850922c63fc0cc1762e
 Init:		false
Resources:
Endpoint Mode:	vip
  • To get detailed information about swarm node
$ docker node inspect w45sgx9gjpijtrq445avrd9wt --pretty
ID:			w45sgx9gjpijtrq445avrd9wt
Hostname:              	plakhera12c.mylabserver.com
Joined at:             	2019-10-20 02:22:41.100359712 +0000 utc
Status:
 State:			Ready
 Availability:         	Active
 Address:		172.31.21.46
Manager Status:
 Address:		172.31.21.46:2377
 Raft Status:		Reachable
 Leader:		Yes
Platform:
 Operating System:	linux
 Architecture:		x86_64
Resources:
 CPUs:			2
 Memory:		1.758GiB
Plugins:
 Log:		awslogs, fluentd, gcplogs, gelf, journald, json-file, local, logentries, splunk, syslog
 Network:		bridge, host, ipvlan, macvlan, null, overlay
 Volume:		local
Engine Version:		19.03.4
TLS Info:
 TrustRoot:
-----BEGIN CERTIFICATE-----
MIIBajCCARCgAwIBAgIUYcja4nW8LxQTgHT55HprKcVObKcwCgYIKoZIzj0EAwIw
EzERMA8GA1UEAxMIc3dhcm0tY2EwHhcNMTkxMDIwMDIxODAwWhcNMzkxMDE1MDIx
ODAwWjATMREwDwYDVQQDEwhzd2FybS1jYTBZMBMGByqGSM49AgEGCCqGSM49AwEH
A0IABLA2Aq+5HrMLbYu7syTQI0oDymK5/NcWHha9wRTM7QIyLa5m56gdCUEsOLsx
ix+Z9GGqktMkXcUNeDPHEIBEqTCjQjBAMA4GA1UdDwEB/wQEAwIBBjAPBgNVHRMB
Af8EBTADAQH/MB0GA1UdDgQWBBTGdeR1vi2EEMYDUd59DxBNy6eD7zAKBggqhkjO
PQQDAgNIADBFAiAjsJzklv8iM5yQhxjYnz9UD8gJ6uCUim/LS/7YzykhGwIhAObX
z2rDu64/DOldMibzX7rBb/u0W4BTiaHudA+2Xpbs
-----END CERTIFICATE-----

 Issuer Subject:	MBMxETAPBgNVBAMTCHN3YXJtLWNh
 Issuer Public Key:	MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEsDYCr7keswtti7uzJNAjSgPKYrn81xYeFr3BFMztAjItrmbnqB0JQSw4uzGLH5n0YaqS0yRdxQ14M8cQgESpMA==

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