This post shows how to add host-entries onto /etc/hosts on docker container when it is run. For the purpose of this post, we are using CentOS/RHEL 7 host. But this should work on any Linux host capable of running latest docker versions. Generally speaking, /etc/hosts file can not be modified before running the docker container. However, current docker has an option "--add-host" which adds host-entries onto /etc/hosts when the container is run. Below is the syntax to add host entry while … [Read more...] about How to add new host entry in /etc/hosts when a docker container is run
DevOps
How to Configure Nagios NRPE Client for System Monitoring (CentOS/RHEL)
Question: How to configure CentOS/RHEL system as Nagios NRPE Client so it can be monitored from Nagios-Server for system health/performance? Enable EPEL REPO (Fedora Repository) and Install Required Packages 1. Download the epel repository packages for CentOS/RHEL 5 and 6. FOR CentOS/RHEL 6: # wget http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm For CentOS/RHEL 5: # wget http://dl.fedoraproject.org/pub/epel/5/x86_64/epel-release-5-4.noarch.rpm 2. Install … [Read more...] about How to Configure Nagios NRPE Client for System Monitoring (CentOS/RHEL)
How to Trace Python Scripts using trace.py
More and more scripts for administrative tasks on Linux OS are written by Python. This post aims to introduce a tool to trace Python statement execution. Python is a dynamic object-oriented programming language which can be used to develop various types of software. It offers strong support for integration with other languages and tools and comes with extensive standard libraries. In Linux distributions, Python is widely used to write administrative tools, such as printer configuration package … [Read more...] about How to Trace Python Scripts using trace.py
How to Access Docker Container’s Network Namespace from Host
This post is to illustrate how to access the docker container's network namespace. 1. Identify the docker container id you want to access and run below command as root on host. # docker ps 2. Get docker container's PID: # pid=$(docker inspect -f '{{.State.Pid}}' ${container_id}) 3. Create netns directory: # mkdir -p /var/run/netns/ 4. Create the name space softlink: # ln -sfT /proc/$pid/ns/net /var/run/netns/[container_id] 5. Run ip netns command to access this name … [Read more...] about How to Access Docker Container’s Network Namespace from Host
How To Change The Time Zone For A Docker Container
The goal of this post is to set up the timezone on the container to match the same timezone on the Docker server, this will allow users to see the same time in both instances (Docker Server and Container). Most of the time Containers do not use the same time as the Docker server, this post will show how to configure this. This is how this looks like before making the changes. Container Time: # docker exec 15c0c99b5c65 date Wed Aug 23 15:40:24 UTC 2019 Docker Server Time: # date Wed … [Read more...] about How To Change The Time Zone For A Docker Container
How To Access Kubernetes Dashboard Externally
Following is an alternative workaround to access Dashboard externally. 1. kubernetes-dashboard is a service file which provides dash-board functionality, to edit this we need to edit dashboard service and change service "type" from ClusterIP to NodePort: [root@kubeXXXX]# kubectl -n kube-system edit service kubernetes-dashboard # Please edit the object below. Lines beginning with a '#' will be ignored, # and an empty file will abort the edit. If an error occurs while saving this file will … [Read more...] about How To Access Kubernetes Dashboard Externally
New User Failed Run Kubectl with Error “The connection to the server xxx.xxx.xxx was refused – did you specify the right host or port?”
The Problem When run kubectl from a new created user, failed with error: The connection to the server xxx.xxx.xxx was refused - did you specify the right host or port? The Solution A newly created user has no KUBECONFIG configured. Setup kubernetes configuration for the new user: # mkdir -p $HOME/.kube # sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config # sudo chown $(id -u):$(id -g) $HOME/.kube/config … [Read more...] about New User Failed Run Kubectl with Error “The connection to the server xxx.xxx.xxx was refused – did you specify the right host or port?”
How to schedule master node running pod/service as a worker node
Question: How can I schedule master node running pod/service as worker node? By deafult, only worker node could run the pod, master only response for the scheduler/configuration. $ kubectl get nodes -o json | jq .items[].spec.taints [ { "effect": "NoSchedule", "key": "node-role.kubernetes.io/master" } ] $ kubectl get nodes -o json | grep master "node-role.kubernetes.io/master": "" "key": … [Read more...] about How to schedule master node running pod/service as a worker node
Endpoint is not Created for Service in Kubernetes
The Problem Endpoints shows 'none': $ kubectl get svc NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE kubernetes ClusterIP 10.yy.0.1 <none> 443/TCP 9d test ClusterIP 10.xx.97.97 <none> 6379/TCP 21s $ kubectl describe svc test Name: test Namespace: default Labels: <none> Annotations: … [Read more...] about Endpoint is not Created for Service in Kubernetes
Troubleshooting kubectl Error: The connection to the server x.x.x.x:6443 was refused – did you specify the right host or port?
This document describes steps to troubleshoot kubectl error: The connection to the server x.x.x.x:6443 was refused - did you specify the right host or port? 1. The kubectl should be executed on the Master Node. 2. Current user must have Kubernetes cluster configuration environment variable (Details of how to are listed under section Preparing to Use Kubernetes as a Regular User), e.g.: $ env | grep -i kube KUBECONFIG=/root/.kube/config 3. The docker service must be running: $ … [Read more...] about Troubleshooting kubectl Error: The connection to the server x.x.x.x:6443 was refused – did you specify the right host or port?