Kubenetes: Is it possible to hit multiple pods with a single request in Kubernetes cluster

Provided you got kubectl in your pod and have access to the api-server, you can get all endpoint adressess and pass them to curl:

kubectl get endpoints <servicename> \
        -o jsonpath="{.subsets[*].addresses[*].ip}" | xargs curl

Alternative without kubectl in pod:

the recommended way to access the api server from a pod is by using kubectl proxy: https://kubernetes.io/docs/tasks/access-application-cluster/access-cluster/#accessing-the-api-from-a-pod this would of course add at least the same overhead. alternatively you could directly call the REST api, you'd have to provide the token manually.

APISERVER=$(kubectl config view --minify | grep server | cut -f 2- -d ":" | tr -d " ")
TOKEN=$(kubectl describe secret $(kubectl get secrets \
     | grep ^default | cut -f1 -d ' ') | grep -E '^token' | cut -f2 -d':' | tr -d " ")

if you provide the APISERVER and TOKEN variables, you don't need kubectl in your pod, this way you only need curl to access the api server and "jq" to parse the json output:

curl $APISERVER/api/v1/namespaces/default/endpoints --silent \
     --header "Authorization: Bearer $TOKEN" --insecure \
     | jq -rM ".items[].subsets[].addresses[].ip" | xargs curl

UPDATE (final version)

APISERVER usually can be set to kubernetes.default.svc and the token should be available at /var/run/secrets/kubernetes.io/serviceaccount/token in the pod, so no need to provide anything manually:

TOKEN=$(cat /var/run/secrets/kubernetes.io/serviceaccount/token); \
curl https://kubernetes.default.svc/api/v1/namespaces/default/endpoints --silent \
     --header "Authorization: Bearer $TOKEN" --insecure \
     | jq -rM ".items[].subsets[].addresses[].ip" | xargs curl

jq is available here: https://stedolan.github.io/jq/download/ (< 4 MiB, but worth it for easily parsing JSON)

I have had the similar situation. Here is how I resolved it (I'm using a namespace other than "default").

Setup access to cluster Using RBAC Authorization

Access to API is done by creating a ServiceAccount, assign it to the Pod and bind a Role to it.

1.Create a ServiceAccount

apiVersion: v1
kind: ServiceAccount
metadata:
  name: my-serviceaccount
  namespace: my-namespace

2.Create a Role: in this section you need to provide the list of resources and the list of actions you'd like to have access to. Here is the example where you'd like to list the endpoints and also get the details of a specific endpoint.

apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: my-role
  namespace: my-namespace
rules:
- apiGroups: [""]
  resources: ["endpoints"]
  verbs: ["get", "list"]

3.Bind the role to the service account

apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: my-role-binding
  namespace: my-namespace
subjects:
- kind: ServiceAccount
  name: my-serviceaccount
roleRef:
  kind: Role
  name: my-role
  apiGroup: rbac.authorization.k8s.io

4.Assign the service account to the pods in your deployment (it should be under template.spec)

apiVersion: apps/v1
kind: Deployment
metadata:
  name: my-deployment
  namespace: my-namespace
spec:
  replicas: 1
  selector:
    matchLabels:
          app: my-pod
  template:
    metadata:
      labels:
        app: my-pod
    spec:
      serviceAccountName: my-serviceaccount
      containers:
      - name: my-pod
        ...

Access Clusters Using the Kubernetes API

Having all the security aspects set, you will have enough privilege to access the API within your Pod. All the required information to communicate with API Server is mounted under /var/run/secrets/kubernetes.io/serviceaccount in your Pod. You can use the following shell script (probably add it to your COMMAND or ENTRYPOINT of the Docker image).

#!/bin/bash
# Point to the internal API server hostname
API_SERVER=https://kubernetes.default.svc

# Path to ServiceAccount token
SERVICE_ACCOUNT=/var/run/secrets/kubernetes.io/serviceaccount

# Read this Pod's namespace
NAMESPACE=$(cat ${SERVICE_ACCOUNT}/namespace)

# Read the ServiceAccount bearer token
TOKEN=$(cat ${SERVICE_ACCOUNT}/token)

# Reference the internal certificate authority (CA)
CA_CERT=${SERVICE_ACCOUNT}/ca.crt

From this point forward, it is just simple REST API call. You can read these environment variables in any language of your choice and access to API.

Here is an example of listing the endpoint for your use case

# List all the endpoints in the namespace that Pod is running
curl --cacert ${CA_CERT} --header "Authorization: Bearer ${TOKEN}" -X GET \
  "${API_SERVER}/api/v1/namespaces/${NAMESPACE}/endpoints"

# List all the endpoints in the namespace that Pod is running for a deployment
curl --cacert ${CA_CERT} --header "Authorization: Bearer ${TOKEN}" -X GET \
  "${API_SERVER}/api/v1/namespaces/${NAMESPACE}/endpoints/my-deployment"

For more information on available API endpoints and how to call them, refer to API Reference.

For those of you trying to find an alternative, I have used hazelcast as distributed event listener. Added a similar POC on github: https://github.com/vinrar/HazelcastAsEventListener