Docker Engine includes swarm mode for natively managing a cluster of Docker Engines called a Swarm. Use the Docker CLI to create a swarm, deploy application services to a swarm, and manage swarm behavior. Complete details at: https://docs.docker.com/engine/swarm/. It’s important to understand the Swarm mode key concepts of Swarm, Node, Service, Task and Load Balancing.
Swarm is typically a cluster of multiple Docker Engines. But for simplicity we’ll run a single node Swarm.
Initialize Swarm mode using the following command:
docker swarm init
This starts a Swarm Manager. By default, manager node are also worker but can be configured to be manager-only.
Find some information about this one-node cluster using the command docker info
Containers: 0
Running: 0
Paused: 0
Stopped: 0
Images: 17
Server Version: 1.13.0
Storage Driver: overlay2
Backing Filesystem: extfs
Supports d_type: true
Native Overlay Diff: true
Logging Driver: json-file
Cgroup Driver: cgroupfs
Plugins:
Volume: local
Network: bridge host ipvlan macvlan null overlay
Swarm: active
NodeID: 92mydh0e09ba5hx3wtmcmvktz
Is Manager: true
ClusterID: v68ikyaff7rdxpaw1j0c9i60s
Managers: 1
Nodes: 1
Orchestration:
Task History Retention Limit: 5
Raft:
Snapshot Interval: 10000
Number of Old Snapshots to Retain: 0
Heartbeat Tick: 1
Election Tick: 3
Dispatcher:
Heartbeat Period: 5 seconds
CA Configuration:
Expiry Duration: 3 months
Node Address: 192.168.65.2
Manager Addresses:
192.168.65.2:2377
Runtimes: runc
Default Runtime: runc
Init Binary: docker-init
containerd version: 03e5862ec0d8d3b3f750e19fca3ee367e13c090e
runc version: 2f7393a47307a16f8cee44a37b262e8b81021e3e
init version: 949e6fa
Security Options:
seccomp
Profile: default
Kernel Version: 4.9.5-moby
Operating System: Alpine Linux v3.5
OSType: linux
Architecture: x86_64
CPUs: 4
Total Memory: 1.952 GiB
Name: moby
ID: SGCM:KDRD:G3M7:PZHN:J4RL:VFFR:G2SR:EKD5:JV4J:RL3X:LF7T:XF6V
Docker Root Dir: /var/lib/docker
Debug Mode (client): false
Debug Mode (server): true
File Descriptors: 31
Goroutines: 124
System Time: 2017-01-27T08:25:58.032295342Z
EventsListeners: 1
No Proxy: *.local, 169.254/16
Username: arungupta
Registry: https://index.docker.io/v1/
Experimental: true
Insecure Registries:
127.0.0.0/8
Live Restore Enabled: falseThis cluster has 1 node, and that is a manager.
This section describes how to deploy a multi-container application using Docker Compose to Swarm mode use Docker CLI.
Create a new directory and cd to it:
mkdir webapp cd webapp
Create a new Compose definition docker-compose.yml using the configuration file shown below.
version: '3'
services:
web:
image: arungupta/couchbase-javaee:travel
environment:
- COUCHBASE_URI=db
ports:
- 8080:8080
- 9990:9990
depends_on:
- db
db:
image: arungupta/couchbase:travel
ports:
- 8091:8091
- 8092:8092
- 8093:8093
- 11210:11210In this Compose file:
-
arungupta/couchbase-javaee:travelimage is WildFly application server with a Java EE application predeployed.COUCHBASE_URIenvironment variable is used to read the host address of Couchbase server.depends_onensures thatwebservice starts beforedbservice. This only ensures that the container is started first but the application readiness needs to be ensured within the application itself. -
arungupta/couchbase-javaee:travelimage is used for Couchbase server. This image pre-configures the Couchbase server and loadstravel-samplebucket with ~32k JSON documents.
This application can be started as:
docker stack deploy --compose-file=docker-compose.yml webapp
This shows the output as:
Creating network webapp_default
Creating service webapp_web
Creating service webapp_dbWildFly and Couchbase services are started on this node. Each service has a single container. If the Swarm mode is enabled on multiple nodes then the containers will be distributed across multiple nodes.
A new overlay network is created. This allows multiple containers on different hosts to communicate with each other.
Verify that the WildFly and Couchbase services are running using docker service ls:
ID NAME MODE REPLICAS IMAGE
a9pkiziw3vgw webapp_db replicated 1/1 arungupta/couchbase:travel
hr5s6ue54kwj webapp_web replicated 1/1 arungupta/couchbase-javaee:travelMore details about the service can be obtained using docker service inspect webapp_web:
[
{
"ID": "z4ljnqteeqwnqcd8kwc5pod5k",
"Version": {
"Index": 2611
},
"CreatedAt": "2017-02-01T23:12:34.84286773Z",
"UpdatedAt": "2017-02-01T23:12:34.86880268Z",
"Spec": {
"Name": "webapp_web",
"Labels": {
"com.docker.stack.namespace": "webapp"
},
"TaskTemplate": {
"ContainerSpec": {
"Image": "arungupta/couchbase-javaee:travel@sha256:7749f40f590108b76e0cbb7967d39e0a9d3637627fd8eb2be5ce53bdda060fcd",
"Labels": {
"com.docker.stack.namespace": "webapp"
},
"Env": [
"COUCHBASE_URI=db"
]
},
"Resources": {},
"Placement": {},
"ForceUpdate": 0
},
"Mode": {
"Replicated": {
"Replicas": 1
}
},
"Networks": [
{
"Target": "s2b2qevxus1la21ebjseaj5g6",
"Aliases": [
"web"
]
}
],
"EndpointSpec": {
"Mode": "vip",
"Ports": [
{
"Protocol": "tcp",
"TargetPort": 8080,
"PublishedPort": 8080,
"PublishMode": "ingress"
},
{
"Protocol": "tcp",
"TargetPort": 9990,
"PublishedPort": 9990,
"PublishMode": "ingress"
}
]
}
},
"Endpoint": {
"Spec": {
"Mode": "vip",
"Ports": [
{
"Protocol": "tcp",
"TargetPort": 8080,
"PublishedPort": 8080,
"PublishMode": "ingress"
},
{
"Protocol": "tcp",
"TargetPort": 9990,
"PublishedPort": 9990,
"PublishMode": "ingress"
}
]
},
"Ports": [
{
"Protocol": "tcp",
"TargetPort": 8080,
"PublishedPort": 8080,
"PublishMode": "ingress"
},
{
"Protocol": "tcp",
"TargetPort": 9990,
"PublishedPort": 9990,
"PublishMode": "ingress"
}
],
"VirtualIPs": [
{
"NetworkID": "x3u7booiccfteittu8qidfel0",
"Addr": "10.255.0.2/16"
},
{
"NetworkID": "s2b2qevxus1la21ebjseaj5g6",
"Addr": "10.0.0.2/24"
}
]
},
"UpdateStatus": {
"StartedAt": "0001-01-01T00:00:00Z",
"CompletedAt": "0001-01-01T00:00:00Z"
}
}
]Logs for the service can be seen using docker service logs -f webapp_web:
webapp_web.1.wby0b04t7bap@moby | =========================================================================
webapp_web.1.wby0b04t7bap@moby |
webapp_web.1.wby0b04t7bap@moby | JBoss Bootstrap Environment
webapp_web.1.wby0b04t7bap@moby |
webapp_web.1.wby0b04t7bap@moby | JBOSS_HOME: /opt/jboss/wildfly
webapp_web.1.wby0b04t7bap@moby |
webapp_web.1.wby0b04t7bap@moby | JAVA: /usr/lib/jvm/java/bin/java
webapp_web.1.wby0b04t7bap@moby |
webapp_web.1.wby0b04t7bap@moby | JAVA_OPTS: -server -Xms64m -Xmx512m -XX:MetaspaceSize=96M -XX:MaxMetaspaceSize=256m -Djava.net.preferIPv4Stack=true -Djboss.modules.system.pkgs=org.jboss.byteman -Djava.awt.headless=true
webapp_web.1.wby0b04t7bap@moby |
webapp_web.1.wby0b04t7bap@moby | =========================================================================
. . .
webapp_web.1.wby0b04t7bap@moby | 23:14:15,811 INFO [org.jboss.as.server] (ServerService Thread Pool -- 34) WFLYSRV0010: Deployed "airlines.war" (runtime-name : "airlines.war")
webapp_web.1.wby0b04t7bap@moby | 23:14:16,076 INFO [org.jboss.as] (Controller Boot Thread) WFLYSRV0060: Http management interface listening on http://127.0.0.1:9990/management
webapp_web.1.wby0b04t7bap@moby | 23:14:16,077 INFO [org.jboss.as] (Controller Boot Thread) WFLYSRV0051: Admin console listening on http://127.0.0.1:9990
webapp_web.1.wby0b04t7bap@moby | 23:14:16,077 INFO [org.jboss.as] (Controller Boot Thread) WFLYSRV0025: WildFly Full 10.1.0.Final (WildFly Core 2.2.0.Final) started in 98623ms - Started 443 of 691 services (404 services are lazy, passive or on-demand)Make sure to wait for the last log statement to show.
Now that the WildFly and Couchbase servers have been configured, let’s access the application. You need to specify IP address of the host where WildFly is running (localhost in our case).
The endpoint can be accessed in this case as:
curl -v http://localhost:8080/airlines/resources/airline
The output is shown as:
* Trying ::1...
* Connected to localhost (::1) port 8080 (#0)
> GET /airlines/resources/airline HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.43.0
> Accept: */*
>
< HTTP/1.1 200 OK
< Connection: keep-alive
< X-Powered-By: Undertow/1
< Server: WildFly/10
< Content-Type: application/octet-stream
< Content-Length: 1402
< Date: Wed, 01 Feb 2017 03:04:41 GMT
<
* Connection #0 to host localhost left intact
[{"travel-sample":{"country":"United States","iata":"Q5","callsign":"MILE-AIR","name":"40-Mile Air","icao":"MLA","id":10,"type":"airline"}}, {"travel-sample":{"country":"United States","iata":"TQ","callsign":"TXW","name":"Texas Wings","icao":"TXW","id":10123,"type":"airline"}}, {"travel-sample":{"country":"United States","iata":"A1","callsign":"atifly","name":"Atifly","icao":"A1F","id":10226,"type":"airline"}}, {"travel-sample":{"country":"United Kingdom","iata":null,"callsign":null,"name":"Jc royal.britannica","icao":"JRB","id":10642,"type":"airline"}}, {"travel-sample":{"country":"United States","iata":"ZQ","callsign":"LOCAIR","name":"Locair","icao":"LOC","id":10748,"type":"airline"}}, {"travel-sample":{"country":"United States","iata":"K5","callsign":"SASQUATCH","name":"SeaPort Airlines","icao":"SQH","id":10765,"type":"airline"}}, {"travel-sample":{"country":"United States","iata":"KO","callsign":"ACE AIR","name":"Alaska Central Express","icao":"AER","id":109,"type":"airline"}}, {"travel-sample":{"country":"United Kingdom","iata":"5W","callsign":"FLYSTAR","name":"Astraeus","icao":"AEU","id":112,"type":"airline"}}, {"travel-sample":{"country":"France","iata":"UU","callsign":"REUNION","name":"Air Austral","icao":"REU","id":1191,"type":"airline"}}, {"travel-sample":{"country":"France","iata":"A5","callsign":"AIRLINAIR","name":"Airlinair","icao":"RLA","id":1203,"type":"airline"}}]This shows 10 airlines from the travel-sample bucket.
Complete set of commands are shown at https://github.com/docker/labs/blob/master/developer-tools/java/chapters/ch05-compose.adoc#access-application.
If you only want to stop the application temporarily while keeping any networks that were created as part of this application, the recommended way is to set the amount of service replicas to 0.
docker service scale webapp_db=0 webapp_web=0
This is especially useful if the stack contains volumes and you want to keep the data. It allows you to simply start the stack again with setting the replicas to a number higher than 0.
Shutdown the application using docker stack rm webapp:
Removing service webapp_db
Removing service webapp_web
Removing network webapp_defaultThis stops the container in each service and removes the services. It also deletes any networks that were created as part of this application.