Service host/port undefined, Kubernetes/Google Container Engine - docker

Question

I have a service with the name mongodb. According to the documentation, the service host and port should be available to other pods in the same cluster through $MONGODB_SERVICE_HOST and $MONGODB_SERVICE_PORT.
However, neither of these are set in my frontend pods. What are the requirements for this to work?
frontend-controller.json
{
"id": "frontend",
"kind": "ReplicationController",
"apiVersion": "v1beta1",
"desiredState": {
"replicas": 1,
"replicaSelector": {"name": "spatula", "role": "frontend"},
"podTemplate": {
"desiredState": {
"manifest": {
"version": "v1beta1",
"id": "frontend",
"containers": [{
"name": "frontend",
"image": "gcr.io/crafty_apex_841/spatula_frontend",
"cpu": 100,
"ports": [{"name": "spatula-server", "containerPort": 80}]
}]
}
},
"labels": { "name": "spatula", "role": "frontend" }
}
},
"labels": { "name": "spatula", "role": "frontend" }
}
frontend-service.json
{
"apiVersion": "v1beta1",
"kind": "Service",
"id": "frontend",
"port": 80,
"containerPort": "spatula-server",
"labels": { "name": "spatula", "role": "frontend" },
"selector": { "name": "spatula", "role": "frontend" },
"createExternalLoadBalancer": true
}
mongodb-service.json
{
"apiVersion": "v1beta1",
"kind": "Service",
"id": "mongodb",
"port": 27017,
"containerPort": "mongodb-server",
"labels": { "name": "spatula", "role": "mongodb" },
"selector": { "name": "spatula", "role": "mongodb" }
}
mongodb-controller.json
{
"id": "mongodb",
"kind": "ReplicationController",
"apiVersion": "v1beta1",
"desiredState": {
"replicas": 1,
"replicaSelector": {"name": "spatula", "role": "mongodb"},
"podTemplate": {
"desiredState": {
"manifest": {
"version": "v1beta1",
"id": "mongodb",
"containers": [{
"name": "mongodb",
"image": "dockerfile/mongodb",
"cpu": 100,
"ports": [{"name": "mongodb-server", "containerPort": 27017}]
}]
}
},
"labels": { "name": "spatula", "role": "mongodb" }
}
},
"labels": { "name": "spatula", "role": "mongodb" }
}
The service:
$ gcloud preview container services list
NAME LABELS SELECTOR IP PORT
mongodb name=spatula,role=mongodb name=spatula,role=mongodb 10.111.240.154 27017
The pod:
$ gcloud preview container pods list
POD IP CONTAINER(S) IMAGE(S) HOST LABELS STATUS
9ffd980f-ab56-11e4-ad76-42010af069b6 10.108.0.11 mongodb dockerfile/mongodb k8s-spatula-node-1.c.crafty-apex-841.internal/104.154.44.77 name=spatula,role=mongodb Running

Answer 1

Because environment variables for pods are only created when the pod is started, the service has to exist before a given pod in order for that pod to see the service's environment variables. You should be able to see them from all new pods you create.
If you'd like to learn more, additional explanation of how services work can be found in the documentation.
Alternatively, all newly created clusters in Container Engine (version 0.9.2 and above) have a SkyDNS service running in the cluster that you can use to access services from pods, even those without the environment variables.