Changing amount of replicas for swarm produces more changes than expected

General Information

docker-java version: 3.1.0-SNAPSHOT docker-compose version: docker-compose version 1.17.1, build 6d101fb docker version: Docker version 17.09.0-ce, build afdb6d4

Problem

Iterating over my services received via DockerClient#listServicesCmd() and then scaling them up with

/* some example code to explain - variable "service" is a service from the iteration and "dockerClient" is an instance of  DockerClient */
ServiceSpec serviceSpec = service.getSpec();
ServiceModeConfig serviceModeConfig = service.getSpec().getMode();
ServiceReplicatedModeOptions serviceReplicatedModeOptions = service.getSpec().getMode().getReplicated().withReplicas(2);
serviceModeConfig = serviceModeConfig.withReplicated(serviceReplicatedModeOptions);
serviceSpec = serviceSpec.withMode(serviceModeConfig);
dockerClient.updateServiceCmd(service.getId(), serviceSpec).withVersion(service.getVersion().getIndex()).exec();

produces an interesting diff:

  "Spec": {
    "Name": "<NAME>",
    "Labels": {
      "com.docker.stack.image": "<IMAGE_NAMESPACE>/<IMAGE_NAME>",
      "com.docker.stack.namespace": "<NAMESPACE>"
    },
    "TaskTemplate": {
      "ContainerSpec": {
        "Image": "<IMAGE_NAMESPACE>/<IMAGE_NAME>:latest",
        "Labels": {
          "com.docker.stack.namespace": "<NAMESPACE>"
        },
        "Env": [],
-       "Privileges": {
-         "CredentialSpec": null,
-         "SELinuxContext": null
-        },
        "TTY": true,
-       "OpenStdin": true,
-       "StopGracePeriod": 60000000000
+       "StopGracePeriod": 10000000000,
+       "DNSConfig": {}
        },
        "Resources": {
          "Limits": {
            "MemoryBytes": 536870912
          }
        },
        "RestartPolicy": {
          "Condition": "none",
          "Delay": 5000000000,
          "MaxAttempts": 3,
          "Window": 20000000000
        },
        "Placement": {},
-       "Networks": [{
-         "Target": "fzmfcwseizy9l7xtbbeq8fuh8",
-         "Aliases": [
-           "hub"
-         ]
-       }],
        "ForceUpdate": 0,
        "Runtime": "container"
      },
      "Mode": {
        "Replicated": {
-         "Replicas": 0
+         "Replicas": 2
        }
+     },
+     "UpdateConfig": {
+       "Parallelism": 1,
+       "FailureAction": "pause",
+       "Monitor": 5000000000,
+       "MaxFailureRatio": 0,
+       "Order": "stop-first"
+     },
+     "RollbackConfig": {
+       "Parallelism": 1,
+       "FailureAction": "pause",
+       "Monitor": 5000000000,
+       "MaxFailureRatio": 0,
+       "Order": "stop-first"
      },
      "EndpointSpec": {
       "Mode": "vip"
      }
    }
-   "Endpoint": {
-     "Spec": {
-        "Mode": "vip"
-     }
-   }

I thought, just the amount of replicas ("Replicas": 0 to "Replicas": 2) would change. Why are there so many other changes? For me, especially the missing network part is a problem. Maybe someone has an idea why this is happening or has proper working code for scaling the amount of a service’s replicas.

[fengxx]

Actually it is not documented https://docs.docker.com/engine/api/v1.30/#operation/ServiceUpdate you has to decipher it yourself.

Edit /etc/docker/daemon.json to add "debug": true, then update service using docker cli, and monitor /var/log/message for the request body, sample I tried docker service update --replicate 3 worker and got below request

Dec  5 10:52:55 x dockerd: time="2017-12-05T10:52:55.307104030-05:00" level=debug msg="form data: {\"EndpointSpec\":{\"Mode\":\"vip\"},\"Labels\":{},\"Mode\":{\"Replicated\":{\"Replicas\":3}},
\"Name\":\"worker\",\"TaskTemplate\":{\"ContainerSpec\":{\"DNSConfig\":{},\"Image\":\"busybox:latest@sha256:bbc3a03235220b170ba48a157dd097dd1379299370e1ed99ce976df0355d24f0\"},\"ForceUpdate\":0,\"Placement\":{\"Platforms\":[{\"Architecture\":\"amd64\",\"OS\":\"linux\"},{\"OS\":\"linux\"},{\"OS\":\"linux\"},{\"OS\":\"linux\"},{\"Architecture\":\"arm64\",\"OS\":\"linux\"},{\"Architecture\":\"386\",\"OS\":\"linux\"},{\"Architecture\":\"ppc64le\",\"OS\":\"linux\"},{\"Architecture\":\"s390x\",\"OS\":\"linux\"}]},\"Resources\":{\"Limits\":{},\"Reservations\":{}},\"Runtime\":\"container\"}}"

[jaschaio]

@sebastianbinder I encountered the same question as you working with the docker API. Do I have to specify everything as upon service creation or is it possible updating only a single thing of the service, for example the name?