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Here are some Key Commands for nginx that I find so usefull. $ nginx -t * Check if Nginx configuration is ok $ nginx -s reload * Gracefully reload NGINX processes $ nginx -V * a like -v, but with more detailed information $ nginx -T * Dump full NGINX configuration $ nginx -g * Display nginx help menu * After config change, test and reload: $ nginx -t && nginx -s reload
 How Kubernetes works Reference link How Kubernetes works | Cloud Native Computing Foundation (cncf.io) Enter Kubernetes, a container orchestration system – a way to manage the lifecycle of containerized applications across an entire fleet. It’s a sort of meta-process that grants the ability to automate the deployment and scaling of several containers at once. Several containers running the same application are grouped together. These containers act as replicas, and serve to load balance incoming requests. A container orchestrator, then, supervises these groups, ensuring that they are operating correctly.    A container orchestrator is essentially an administrator in charge of operating a fleet of containerized applications. If a container needs to be restarted or acquire more resources, the orchestrator takes care of it for you. That’s a fairly broad outline of how most container orchestrators work. Let’s take a deeper look at all the specific components of Kubernetes that make this happen. Kubernetes terminology and architectureKubernetes introduces a lot of vocabulary to describe how your application is organized. We’ll start from the smallest layer and work our way up. PodsA Kubernetes pod is a group of containers, and is the smallest unit that Kubernetes administers. Pods have a single IP address that is applied to every container within the pod. Containers in a pod share the same resources such as memory and storage. This allows the individual Linux containers inside a pod to be treated collectively as a single application, as if all the containerized processes were running together on the same host in more traditional workloads. It’s quite common to have a pod with only a single container, when the application or service is a single process that needs to run. But when things get more complicated, and multiple processes need to work together using the same shared data volumes for correct operation, multi-container pods ease deployment configuration compared to setting up shared resources between containers on your own. For example, if you were working on an image-processing service that created GIFs, one pod might have several containers working together to resize images. The primary container might be running the non-blocking microservice application taking in requests, and then one or more auxiliary (side-car) containers running batched background processes or cleaning up data artifacts in the storage volume as part of managing overall application performance. DeploymentsKubernetes deployments define the scale at which you want to run your application by letting you set the details of how you would like pods replicated on your Kubernetes nodes. Deployments describe the number of desired identical pod replicas to run and the preferred update strategy used when updating the deployment. Kubernetes will track pod health, and will remove or add pods as needed to bring your application deployment to the desired state. ServicesThe lifetime of an individual pod cannot be relied upon; everything from their IP addresses to their very existence are prone to change. In fact, within the DevOps community, there’s the notion of treating servers as either “pets” or “cattle.” A pet is something you take special care of, whereas cows are viewed as somewhat more expendable. In the same vein, Kubernetes doesn’t treat its pods as unique, long-running instances; if a pod encounters an issue and dies, it’s Kubernetes’ job to replace it so that the application doesn’t experience any downtime. A service is an abstraction over the pods, and essentially, the only interface the various application consumers interact with. As pods are replaced, their internal names and IPs might change. A service exposes a single machine name or IP address mapped to pods whose underlying names and numbers are unreliable. A service ensures that, to the outside network, everything appears to be unchanged. NodesA Kubernetes node manages and runs pods; it’s the machine (whether virtualized or physical) that performs the given work. Just as pods collect individual containers that operate together, a node collects entire pods that function together. When you’re operating at scale, you want to be able to hand work over to a node whose pods are free to take it. The Kubernetes control planeThe Kubernetes control plane is the main entry point for administrators and users to manage the various nodes. Operations are issued to it either through HTTP calls or connecting to the machine and running command-line scripts. As the name implies, it controls how Kubernetes interacts with your applications. ClusterA cluster is all of the above components put together as a single unit. Kubernetes componentsWith a general idea of how Kubernetes is assembled, it’s time to take a look at the various software components that make sure everything runs smoothly. Both the control plane and individual worker nodes have three main components each. Control PlaneAPI ServerThe API server exposes a REST interface to the Kubernetes cluster. All operations against pods, services, and so forth, are executed programmatically by communicating with the endpoints provided by it. SchedulerThe scheduler is responsible for assigning work to the various nodes. It keeps watch over the resource capacity and ensures that a worker node’s performance is within an appropriate threshold. Controller managerThe controller-manager is responsible for making sure that the shared state of the cluster is operating as expected. More accurately, the controller manager oversees various controllers which respond to events (e.g., if a node goes down). Worker node componentsKubeletA Kubelet tracks the state of a pod to ensure that all the containers are running. It provides a heartbeat message every few seconds to the control plane. If a replication controller does not receive that message, the node is marked as unhealthy. Kube proxyThe Kube proxy routes traffic coming into a node from the service. It forwards requests for work to the correct containers. etcdis a distributed key-value store that Kubernetes uses to share information about the overall state of a cluster. Additionally, nodes can refer to the global configuration data stored there to set themselves up whenever they are regenerated. Installing Docker CE on Rocky Linux 8Docker has a dedicated CentOS repository that we can apply to Rocky Linux. So, the ideal would be to add it to the system and install it from there. First access your server via SSH or, if you are using Rocky Linux from the desktop, open a terminal. Now install the With this package installed, we can add the Docker repository. Output: If you want to check if the repository has been successfully added, you can run sudo dnf install docker-ce docker-ce-cli containerd.io With this process, Docker is already installed, but its service is not started. To start the Docker service, run It is convenient that the service starts with the system, to do this Output: Finally, you can check the status of the service In conclusion, Docker is installed correctly. First steps with Docker CE on Rocky LinuxUsing Docker requires root permissions. This can be a problem for many people, so a real option would be to add the user to the To complete this, run the following command Now, you can run Docker and for this you can use the test image. mkdir /var/lib/rpm/backup cp -a /var/lib/rpm/__db* /var/lib/rpm/backup/ rm -f /var/lib/rpm/__db.[0-9][0-9]* rpm --quiet -qa rpm --rebuilddb yum clean all Docker is a set of Platform as a Service (PaaS) products that uses operating system level virtualizations to deliver software in the form of containers. Docker CE (Community Edition) is the strip down version of Docker EE (Enterprise Edition). Docker CE is free and open source and distributed under Apache License 2.0. In Red Hat Enterprise Linux (RHEL) 8 / CentOS 8, Support of Docker has been removed by the vendor. Whereas a new containerization platform libpod (Podman’s Container Management Library) has been introduced inplace of Docker. However, we can still install Docker and it’s dependencies on CentOS 8 / RHEL 8 from third party yum repositories. In this article, we are installing Docker CE and docker-compose on CentOS 8. Prerequisites
Environment SpecificationWe have configured a CentOS 8 virtual machine with following specifications.
Adding Docker CE yum Repository on CentOS 8:Connect with docker-01.example.com using ssh as root user. Docker CE is available to download from Docker’s Official Website However, we can also install it from Docker CE yum repository. Add Docker CE yum repository using dnf command. Build cache for Docker yum repository. Installing Docker CE on CentOS 8:After addition of Docker CE yum repository, we can now easily install Docker CE on CentOS 8 by using a dnf command. Docker CE requires containerd.io-1.2.2-3 (or later) package, which is blocked in CentOS 8. Therefore, we have to use an earlier version of containerd.io package. Install docker-ce with an earlier version of containerd.io using following command. Enable and start Docker service. Check status of Docker service. Check Docker version. Docker CE has been installed on CentOS 8. Create a Container using Docker in CentOS 8:Let’s put Docker into action by creating a simple container. For this purpose, we are using official image of Alpine Linux from Docker Hub. Pull Alpine Linux image from Docker Hub. List locally available docker images. Create and run a container using Alpine Linux image. Installing Docker-compose on CentOS 8:Additionally, we are installing docker-compose on our CentOS 8 server, so we can create and run multiple containers as a single service. Download docker-compose package from GitHub. Grant execute permissions to docker-compose command. Check docker-compose version. We have successfully installed Docker CE and Docker-Compose on CentOS 8. We have only explored the installation of Docker CE here One could only guess that the rationale for lack of DNS caching in RHEL is the arguable efficiency for those systems which aren’t network connected or simply don’t need to make any DNS lookups. There are of course such cases where you don’t need (many) DNS resolutions. I can think of:
Those systems will likely issue zero to none DNS lookups while running, and DNS cache isn’t really a thing for them. But for the most intents of running either a desktop or server RHEL machines, you will absolutely benefit from a DNS cache. Enabling DNS cache in RHEL 7 and 8 is easy thanks to The I won’t torture you with long instructions on how to enable the DNS cache. It’s really quick and goes down to: You have just made your machine already faster by running these. For more details and fine-tuning, read on. NetworkManager and dnsmasqLet’s explain what happened when we ran the above commands to enable DNS caching. In the first bit, we have installed the very essential of DNS caching – Then we write out a file, This, in turn, starts a private instance of It doesn’t end there. NetworkManager now updated The Very clean and beautiful integration. Verify dnsmasq is workingSimply perform a DNS lookup using If the output looks like a valid IP address or a list of IP addresses, then You can also check that DNS caching is working. Perform a resolution against another domain by running the following command twice: Observe Subsequent requests yield: See what kind of DNS requests your system makesTo see what DNS request your system makes, you can temporarily enable logging of queries. Note that this will clear DNS cache because You can then dnsmasq[20802]: forwarded logs6.papertrailapp.com to 2606:4700:4700::1001 dnsmasq[20802]: reply logs6.papertrailapp.com is 169.46.82.182 dnsmasq[20802]: reply logs6.papertrailapp.com is 169.46.82.183 dnsmasq[20802]: reply logs6.papertrailapp.com is 169.46.82.184 dnsmasq[20802]: reply logs6.papertrailapp.com is 169.46.82.185 This approach may be used for finding what external sites your server communicates with. Once you’re done, don’t forget to turn off the logging: How well is dnsmasq doing on your systemThe
So we can collect DNS query stats easily: The output may include, for example: The 0 in We also see that 30 DNS lookups were forwarded over to upstream nameservers (misses), while 60 were satisfied directly by cache (hits). Gathering stats like this will work well in case you only have one instance of dnsmasq. Sometimes you have more than one (e.g. libvirt may run one of its own). It is more reliable to use the statistical information of dnsmasq that is exposed, not surprisingly, via DNS ???? The commands: … give you hits and misses, respectively. With some command line magic, you can easily calculate your DNS cache hit-ratio: The output is a percentage of DNS requests that were satisfied by DNS cache, e.g.: 80.95%. Tuning the cache sizeThe default cache size of For a desktop machine, you may want to increase it by large. This will assist with much less home router strain and faster network experience, especially if you’re a Chrome user. This browser does DNS caching of its own, but only as long as 1 minute – the issue that is discarded as a “feature”. So to set DNS cache size to 20k, run: dnsmasq and your desktopTo expand the topic of the desktop use of dnsmasq, you can also leverage it to block tracking scripts and for speeding up your browsing experience: Finally, you may also want to improve the DNS speed by ensuring minimum TTL for DNS records that have it set too low. This will ensure that even if a DNS record is configured with, e.g. 2 minutes TTL on remote nameserver, Note that this is acceptable for desktop machines, but not for web servers: Phew, now I think that’s about it for CentOS 7 non-root users install source version of Docker
cat /etc/group | grep docker sudo groupadd docker cat /etc/group | grep docker useradd test cat /etc/passwd | grep dev01 Add sudo permissions for new users vi /etc/sudoers
gpasswd -a admin docker mkdir /docker tar -zxvf docker-19.03.7.tgz -C /docker cp docker/* /usr/bin/ chown root:docker /usr/bin/docker* ll /usr/bin/ | grep docker vi /etc/systemd/system/docker.service [Unit] [Service] [Install] chmod a+x /etc/systemd/system/docker.service vi /etc/docker/daemon.json { systemctl start docker docker basic commands docker start / stop / restart / view the status View docker has been mirrored in the docker’s official website searches for the specified mirror Download image (without labeling the default download the latest version of the image) Start the container (run the image-based container with the name xxx, and map the container port to the local port, and the container directory file is stored in the local directory) docker run -d -name xxx -p Local port: Container port -v native directory: container directory image name: tag (or ID) into the running container docker exec -it container name (or ID) / bin / bash container start / stop / restart / information / delete docker start / stop / restart / inspect / rm container name (or ID) view running containers docker ps view all containers (including running, stopped, not including deleted) docker ps -a image deletion (before deleting the image Please delete all containers related to this image) docker rmi image name: tag (or ID) view information about currently installed docker docker info yum install -y yum-utils device-mapper-persistent-data lvm2 yum-config-manager –add-repo https://mirrors.aliyun.com/docker-ce/linux/centos/docker-ce.repo yum install docker-ce systemctl enable docker systemctl start docker groupadd docker usermod -aG docker $USER docker volume create portainer_data docker run -d -p 9000:9000 -v /var/run/docker.sock:/var/run/docker.sock -v portainer_data:/data portainer/portainer Docker common commands docker pull -pull images docker rmi -After deleting the image, you can match it directly based on the image name or the first letter of the tag docker start container_id- open container (here can be container id or name) docker stop container_id -stop container (here can be container id or name) docker rm -delete a container (only stopped containers can be deleted) docker build -create images using Dockerfile docker exec -execute commands in the container, for example: docker exec -it container_id (container name or id) / bin / bash (bin / bash command or tool to execute) docker logs –View container logs, for example: docker logs -f -t –tail 10 container_id (container name or id) Run the container docker run -it –rm -p 8000:80 –name aspnet_sample microsoft/dotnet__ –name container name, followed by mirror path or name –rm delete the container after running -p port mapping 8000 external port 80 mirroring running port mapping 8000 to 80 mirroring -it outputs the contents of the container command line, that is, the container’s own program output is a bit similar to the foreground run in the console -d Contrary to it Hide background run LEMP is a software stack that includes a set of free open source tools that are used to power high traffic and dynamic websites. LEMP is an acronym for Linux, Nginx (pronounced Engine X), MariaDB / MySQL, and PHP. Nginx is an open source, powerful and high-performance web server that can also double as a reverse proxy. MariaDB is a database system for storing user data, while PHP is a server-side scripting language for developing and supporting dynamic web pages. Related: In this article, you will learn how to install a LEMP server on a CentOS 8 Linux distribution. Step 1: Update the package on CentOS 8 First, update the repository and packages on CentOS 8 Linux by running the following dnf command. dnf update Step 2: Install Nginx web server on CentOS 8 After the package update is complete, install Nginx with a simple command. dnf install nginx Install Nginx on CentOS 8 The code snippet shows that the installation of Nginx went smoothly without any problems. After the installation is complete, configure Nginx to start automatically at system startup, and verify that Nginx is running by executing a command. systemctl enable nginx nginx -v Step 3: Install MariaDB on CentOS 8 MariaDB is a free and open source branch of MySQL and provides the latest features that make it a better alternative to MySQL. To install MariaDB, run the command. dnf install mariadb-server mariadb -y To make MariaDB start automatically at system startup, run. systemctl start mariadb The MariaDB database engine is not secure and anyone can log in without credentials. To harden MariaDB and protect it to minimize the chance of unauthorized access, run the command. mysql_secure_installation Step 4: Install PHP 7 on CentOS 8 Finally, we will install the last LEMP component, PHP, which is a scripted web programming language that is usually used to develop dynamic web pages. At the time of writing this guide, the latest version is PHP 7.4. We will install it using the Remi repository. The Remi database is a free database that comes with the latest cutting-edge software version and is not available on CentOS by default. Run the following command to install the EPEL repository. dnf install https://dl.Fedoraproject.org/pub/epel/epel-release-latest-8.noarch.rpm dnf install dnf-utils http://rpms.remirepo.net/enterprise/remi-release-8.rpm dnf module list php CentOS-8 – AppStream Remi’s Modular repository for Enterprise Linux 8 – x86_64 dnf module reset php dnf module enable php:remi-7.4 dnf install php php-opcache php-gd php-curl php-mysqlnd php -v systemctl start php-fpm nano /etc/php-fpm.d/www.conf user = apache user = nginx systemctl restart nginx cd /usr/share/nginx/html/ LAMP is an acronym for Linux, Apache, MySQL, and PHP, and is a popular free and open source stack used by webmasters and developers to test and host dynamic websites. Step 1: Update CentOS 8 software package dnf update dnf install httpd httpd-tools systemctl enable httpd systemctl start httpd systemctl status httpd httpd -v rpm -qi httpd centos8 with mariaDB dnf install mariadb-server mariadb -y systemctl start mariadb systemctl enable mariadb mysql_secure_installation dnf install https://dl.Fedoraproject.org/pub/epel/epel-release-latest-8.noarch.rpm dnf install dnf-utils http://rpms.remirepo.net/enterprise/remi-release-8.rpm dnf module list php dnf module reset php dnf module enable php:remi-7.4 dnf install php php-opcache php-gd php-curl php-mysqlnd dnf install php php-opcache php-gd php-curl php-mysqlnd php -v systemctl start php-fpm setsebool -P httpd_execmem 1 systemctl restart httpd |
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