I'm using Openshift and Kubernetes as cloud platform for my application. For test purposes I need to intercept incoming http requests to my pods. Is this possible to do that with Kubernetes client library or maybe it can be configured with yaml?
Simple answer is no, you can't.
One of the ways to overcome this is to exec into your container (kubectl exec -it <pod> bash), install tcpdump and run something like tcpdump -i eth0 -n.
A more reasonable way to have it solved on infra level is to use some tracing tool like Jaeger/Zipkin
You can try something like below it will work. First you need create a job.
Let's say with name (tcpdumppod.yaml)
apiVersion: batch/v1
kind: Job
metadata:
name: tcpdump-capture-job
namespace: blue
spec:
template:
metadata:
name: "tcpdumpcapture-pod"
spec:
hostNetwork: true
nodeSelector:
kubernetes.io/hostname: "ip-xx-x-x-xxx.ap-south-1.compute.internal"
tolerations:
- key: node-role.kubernetes.io/master
effect: NoSchedule
containers:
- name: "job-container"
image: "docker.io/centos/tools"
command: ["/bin/bash", "-c", "--"]
args: [ "tcpdump -i any -s0 -vv -n dst host 10.233.6.70 and port 7776 || src 10.233.64.23" ]
restartPolicy: Never
backoffLimit: 3
activeDeadlineSeconds: 460
=> kubectl create -f tcpdumppod.yaml
And check the pod logs which is created by the job when the container is running.
Related
Scenario is like this:
I have a pod running in a node in K8s cluster in GCP. cluster is created using kops and pod is created using kne_cli.
I know only the name of the pod e.g. "test-pod".
My requirement is to configure something in the node where this pod is running. e.g. I want to update "iptables -t nat" table in node.
how to access the node and configure it from within a pod?
any suggestion will be helpful.
You the Job or deployment or POD, not sure how POD is getting managed. If you just want to run that task Job is good fir for you.
One option is to use SSH way :
You can run one POD inside that you get a list of Nodes or specific node as per need and run SSH command to connect with that node.
That way you will be able to access Node from POD and run commands top of Node.
You can check this document for ref : https://alexei-led.github.io/post/k8s_node_shell/
Option two :
You can mount sh file on Node with IP table command and invoke that shell script from POD to execute which will run the command whenever you want.
Example :
apiVersion: v1
kind: ConfigMap
metadata:
name: command
data:
command.sh: |
#!/bin/bash
echo "running sh script on node..!"
---
apiVersion: batch/v1beta1
kind: CronJob
metadata:
name: command
spec:
schedule: "*/1 * * * *"
jobTemplate:
spec:
template:
spec:
serviceAccountName: cron-namespace-admin
containers:
- name: command
image: IMAGE:v1
imagePullPolicy: IfNotPresent
volumeMounts:
- name: commandfile
mountPath: /test/command.sh
subPath: command.sh
- name: script-dir
mountPath: /test
restartPolicy: OnFailure
volumes:
- name: commandfile
configMap:
name: command
defaultMode: 0777
- name: script-dir
hostPath:
path: /var/log/data
type: DirectoryOrCreate
Use privileged mode
securityContext:
privileged: true
Privileged - determines if any container in a pod can enable
privileged mode. By default a container is not allowed to access any
devices on the host, but a "privileged" container is given access to
all devices on the host. This allows the container nearly all the same
access as processes running on the host. This is useful for containers
that want to use linux capabilities like manipulating the network
stack and accessing devices.
Read more : https://kubernetes.io/docs/concepts/security/pod-security-policy/#privileged
You might be better off using GKE and configuring the ip-masq-agent as described here: https://cloud.google.com/kubernetes-engine/docs/how-to/ip-masquerade-agent
In case you stick with kops on GCE, I would suggest following the guide for ip-masq-agent here instead of the GKE docs: https://kubernetes.io/docs/tasks/administer-cluster/ip-masq-agent/
In case you really need to run custom iptables rules on the host then your best option is to create a DaemonSet with pods that are privileged and have hostNetwork: true. That should allow you to modify iptable rules directly on the host from the pod.
Do I still need to expose pod via clusterip service?
There are 3 pods - main, front, api. I need to allow ingress+egress connection to main pod only from the pods- api and frontend. I also created service-main - service that exposes main pod on port:80.
I don't know how to test it, tried:
k exec main -it -- sh
netcan -z -v -w 5 service-main 80
and
k exec main -it -- sh
curl front:80
The main.yaml pod:
apiVersion: v1
kind: Pod
metadata:
labels:
app: main
item: c18
name: main
spec:
containers:
- image: busybox
name: main
command:
- /bin/sh
- -c
- sleep 1d
The front.yaml:
apiVersion: v1
kind: Pod
metadata:
labels:
app: front
name: front
spec:
containers:
- image: busybox
name: front
command:
- /bin/sh
- -c
- sleep 1d
The api.yaml
apiVersion: v1
kind: Pod
metadata:
labels:
app: api
name: api
spec:
containers:
- image: busybox
name: api
command:
- /bin/sh
- -c
- sleep 1d
The main-to-front-networkpolicy.yaml
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
name: front-end-policy
spec:
podSelector:
matchLabels:
app: main
policyTypes:
- Ingress
- Egress
ingress:
- from:
- podSelector:
matchLabels:
app: front
ports:
- port: 8080
egress:
- to:
- podSelector:
matchLabels:
app: front
ports:
- port: 8080
What am I doing wrong? Do I still need to expose main pod via service? But should not network policy take care of this already?
Also, do I need to write containerPort:80 in main pod? How to test connectivity and ensure ingress-egress works only for main pod to api, front pods?
I tried the lab from ckad prep course, it had 2 pods: secure-pod and web-pod. There was issue with connectivity, the solution was to create network policy and test using netcat from inside the web-pod's container:
k exec web-pod -it -- sh
nc -z -v -w 1 secure-service 80
connection open
UPDATE: ideally I want answers to these:
a clear explanation of the diff btw service and networkpolicy.
If both service and netpol exist - what is the order of evaluation that the traffic/request goes thru? It first goes thru netpol then service? Or vice versa?
if I want front and api pods to send/receive traffic to main - do I need separate services exposing front and api pods?
Network policies and services are two different and independent Kubernetes resources.
Service is:
An abstract way to expose an application running on a set of Pods as a network service.
Good explanation from the Kubernetes docs:
Kubernetes Pods are created and destroyed to match the state of your cluster. Pods are nonpermanent resources. If you use a Deployment to run your app, it can create and destroy Pods dynamically.
Each Pod gets its own IP address, however in a Deployment, the set of Pods running in one moment in time could be different from the set of Pods running that application a moment later.
This leads to a problem: if some set of Pods (call them "backends") provides functionality to other Pods (call them "frontends") inside your cluster, how do the frontends find out and keep track of which IP address to connect to, so that the frontend can use the backend part of the workload?
Enter Services.
Also another good explanation in this answer.
For production you should use a workload resources instead of creating pods directly:
Pods are generally not created directly and are created using workload resources. See Working with Pods for more information on how Pods are used with workload resources.
Here are some examples of workload resources that manage one or more Pods:
Deployment
StatefulSet
DaemonSet
And use services to make requests to your application.
Network policies are used to control traffic flow:
If you want to control traffic flow at the IP address or port level (OSI layer 3 or 4), then you might consider using Kubernetes NetworkPolicies for particular applications in your cluster.
Network policies target pods, not services (an abstraction). Check this answer and this one.
Regarding your examples - your network policy is correct (as I tested it below). The problem is that your cluster may not be compatible:
For Network Policies to take effect, your cluster needs to run a network plugin which also enforces them. Project Calico or Cilium are plugins that do so. This is not the default when creating a cluster!
Test on kubeadm cluster with Calico plugin -> I created similar pods as you did, but I changed container part:
spec:
containers:
- name: main
image: nginx
command: ["/bin/sh","-c"]
args: ["sed -i 's/listen .*/listen 8080;/g' /etc/nginx/conf.d/default.conf && exec nginx -g 'daemon off;'"]
ports:
- containerPort: 8080
So NGINX app is available at the 8080 port.
Let's check pods IP:
user#shell:~$ kubectl get pods -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
api 1/1 Running 0 48m 192.168.156.61 example-ubuntu-kubeadm-template-2 <none> <none>
front 1/1 Running 0 48m 192.168.156.56 example-ubuntu-kubeadm-template-2 <none> <none>
main 1/1 Running 0 48m 192.168.156.52 example-ubuntu-kubeadm-template-2 <none> <none>
Let's exec into running main pod and try to make request to the front pod:
root#main:/# curl 192.168.156.61:8080
<!DOCTYPE html>
...
<title>Welcome to nginx!</title>
It is working.
After applying your network policy:
user#shell:~$ kubectl apply -f main-to-front.yaml
networkpolicy.networking.k8s.io/front-end-policy created
user#shell:~$ kubectl exec -it main -- bash
root#main:/# curl 192.168.156.61:8080
...
Not working anymore, so it means that network policy is applied successfully.
Nice option to get more information about applied network policy is to run kubectl describe command:
user#shell:~$ kubectl describe networkpolicy front-end-policy
Name: front-end-policy
Namespace: default
Created on: 2022-01-26 15:17:58 +0000 UTC
Labels: <none>
Annotations: <none>
Spec:
PodSelector: app=main
Allowing ingress traffic:
To Port: 8080/TCP
From:
PodSelector: app=front
Allowing egress traffic:
To Port: 8080/TCP
To:
PodSelector: app=front
Policy Types: Ingress, Egress
I'm running a pod with 3 containers (telegraf, fluentd and an in-house agent) that makes use of shareProcessNamespace: true.
I've written a python script to fetch the initial config for telegraf and fluentd from a central controller API endpoint. Since this is a one time operation, I plan to use helm post-install hook.
apiVersion: batch/v1
kind: Job
metadata:
name: agent-postinstall
annotations:
"helm.sh/hook-weight": "3"
"helm.sh/hook": "post-install"
spec:
template:
spec:
containers:
- name: agent-postinstall
image: "{{ .Values.image.agent.repository }}:{{ .Values.image.agent.tag | default .Chart.AppVersion }}"
imagePullPolicy: IfNotPresent
command: ['python3', 'getBaseCfg.py']
volumeMounts:
- name: config-agent-volume
mountPath: /etc/config
volumes:
- name: config-agent-volume
configMap:
name: agent-cm
restartPolicy: Never
backoffLimit: 1
It is required for the python script to check if telegraf/fluentd/agent processes are up, before getting the config. I intend to wait (with a timeout) until pgrep <telegraf/fluentd/agent> returns true and then fire APIs. Is there a way to enable shareProcessNamespace for the post-install hook as well? Thanks.
PS: Currently, the agent calls the python script along with its own startup script. It works, but it is kludgy. I'd like to move it out of agent container.
shareProcessNamespace
Most important part of this flag is it works only within one pod, all containers within one pod will share processes between each other.
In described approach job is supposed to be used. Job creates a separate pod so it won't work this way. Container should be a part of the "main" pod with all other containers to have access to running processes of that pod.
More details about process sharing.
Possible way to solution it
It's possible to get processes from the containers directly using kubectl command.
Below is an example how to check state of the processes using pgrep command. The pgrepContainer container needs to have the pgrep command already installed.
job.yaml:
apiVersion: batch/v1
kind: Job
metadata:
name: "{{ .Release.Name }}-postinstall-hook"
annotations: "helm.sh/hook": post-install
spec:
template:
spec:
serviceAccountName: config-user # service account with appropriate permissions is required using this approach
volumes:
- name: check-script
configMap:
name: check-script
restartPolicy: Never
containers:
- name: post-install-job
image: "bitnami/kubectl" # using this image with kubectl so we can connect to the cluster
command: ["bash", "/mnt/script/checkScript.sh"]
volumeMounts:
- name: check-script
mountPath: /mnt/script
And configmap.yaml which contains script and logic which check three processes in loop for 60 iterations per 10 seconds each:
apiVersion: v1
kind: ConfigMap
metadata:
name: check-script
data:
checkScript.sh: |
#!/bin/bash
podName=test
pgrepContainer=app-1
process1=sleep
process2=pause
process3=postgres
attempts=0
until [ $attempts -eq 60 ]; do
kubectl exec ${podName} -c ${pgrepContainer} -- pgrep ${process1} 1>/dev/null 2>&1 \
&& kubectl exec ${podName} -c ${pgrepContainer} -- pgrep ${process2} 1>/dev/null 2>&1 \
&& kubectl exec ${podName} -c ${pgrepContainer} -- pgrep ${process3} 1>/dev/null 2>&1
if [ $? -eq 0 ]; then
break
fi
attempts=$((attempts + 1))
sleep 10
echo "Waiting for all containers to be ready...$[ ${attempts}*10 ] s"
done
if [ $attempts -eq 60 ]; then
echo "ERROR: Timeout"
exit 1
fi
echo "All containers are ready !"
echo "Configuring telegraf and fluentd services"
Final result will look like:
$ kubectl get pods
NAME READY STATUS RESTARTS AGE
test 2/2 Running 0 20m
test-postinstall-hook-dgrc9 0/1 Completed 0 20m
$ kubectl logs test-postinstall-hook-dgrc9
Waiting for all containers to be ready...10 s
All containers are ready !
Configuring telegraf and fluentd services
Above is an another approach, you can use its logic as base to achieve your end goal.
postStart
Also postStart hook can be considered to be used where some logic will be located. It will run after container is created. Since main application takes time to start and there's already logic which waits for it, it's not an issue that:
there is no guarantee that the hook will execute before the container ENTRYPOINT
I am new to Kubernetes I am trying to mimic a behavior a bit like what I do with docker-compose when I serve a Couchbase database in a docker container.
couchbase:
image: couchbase
volumes:
- ./couchbase:/opt/couchbase/var
ports:
- 8091-8096:8091-8096
- 11210-11211:11210-11211
I managed to create a cluster in my localhost using a tool called "kind"
kind create cluster --name my-cluster
kubectl config use-context my-cluster
Then I am trying to use that cluster to deploy a Couchbase service
I created a file named couchbase.yaml with the following content (I am trying to mimic what I do with my docker-compose file).
apiVersion: apps/v1
kind: Deployment
metadata:
name: couchbase
namespace: my-project
labels:
platform: couchbase
spec:
replicas: 1
selector:
matchLabels:
platform: couchbase
template:
metadata:
labels:
platform: couchbase
spec:
volumes:
- name: couchbase-data
hostPath:
# directory location on host
path: /home/me/my-project/couchbase
# this field is optional
type: Directory
containers:
- name: couchbase
image: couchbase
volumeMounts:
- mountPath: /opt/couchbase/var
name: couchbase-data
Then I start the deployment like this:
kubectl create namespace my-project
kubectl apply -f couchbase.yaml
kubectl expose deployment -n my-project couchbase --type=LoadBalancer --port=8091
However my deployment never actually start:
kubectl get deployments -n my-project couchbase
NAME READY UP-TO-DATE AVAILABLE AGE
couchbase 0/1 1 0 6m14s
And when I look for the logs I see this:
kubectl logs -n my-project -lplatform=couchbase --all-containers=true
Error from server (BadRequest): container "couchbase" in pod "couchbase-589f7fc4c7-th2r2" is waiting to start: ContainerCreating
As OP mentioned in a comment, issue was solved using extra mount as explained in documentation: https://kind.sigs.k8s.io/docs/user/configuration/#extra-mounts
Here is OP's comment but formated so it's more readable:
the error shows up when I run this command:
kubectl describe pods -n my-project couchbase
I could fix it by creating a new kind cluster:
kind create cluster --config cluster.yaml
Passing this content in cluster.yaml:
kind: Cluster
apiVersion: kind.x-k8s.io/v1alpha4
name: inf
nodes:
- role: control-plane
extraMounts:
- hostPath: /home/me/my-project/couchbase
containerPath: /couchbase
In couchbase.yaml the path becomes path: /couchbase of course.
I've got a k8n cluster setup on a bare-metal ubuntu 16.04 cluster using weave networking with kubeadm. I'm having a variety of little problems, the most recent of which is that I realized that kube-dns does not resolve external addresses (e.g. google.com). Any thoughts on why? Using kube-adm did not give me a lot of insight into the details of that part of the setup.
The issue turned out to be that a node-level firewall was interfering with the cluster networking. So there was no issue with the DNS setup.
I had the same issue on kubernetes v1.6 and it was not a firewall issue in my case.
The problem was that I have configured the DNS manually on the /etc/docker/daemon.json, and these parameters are not used by kube-dns. Instead it is needed to create a configmap for kubedns (pull request here and documentation here), as follows:
Solution
Create a yaml for the configmap, for example kubedns-configmap.yml
apiVersion: v1
kind: ConfigMap
metadata:
name: kube-dns
namespace: kube-system
data:
upstreamNameservers: |
["<own-dns-ip>"]
And simply, apply it on kubernetes with
kubectl apply -f kubedns-configmap.yml
Test 1
On your kubernetes host node:
dig #10.96.0.10 google.com
Test 2
To test it I use a busybox image with the following resource configuration (busybox.yml):
apiVersion: v1
kind: Pod
metadata:
name: busybox
spec:
containers:
# for arm
#- image: hypriot/armhf-busybox
- image: busybox
command:
- sleep
- "3600"
imagePullPolicy: IfNotPresent
name: busybox
restartPolicy: Always
Apply the resource with
kubectl apply -f busybox.yml
And test it with the following:
kubectl exec -it busybox -- ping google.com