Web Quickstart

In this post, I am going to try Ansistrano to deploy a file on a web server. (See this post  this post  for detail about Ansible) what is Ansistrano? " ansistrano.deploy and ansistrano.rollback are Ansible roles to easily manage the deployment process for scripting applications such as PHP, Python and Ruby. It's an Ansible port for Capistrano." ( https://github.com/ansistrano/deploy ) install %  ansible-galaxy install ansistrano.deploy ansistrano.rollback create test file % mkdir -p public_html  % echo 'hello' > public_html/index.html  deploy % vim playbook.yml --- - name: deploy code hosts: webservers become: true vars: ansistrano_deploy_from: "{{ playbook_dir }}/public_html/" ansistrano_deploy_to: "/var/www/my-app" ansistrano_keep_releases: 3 ansistrano_deploy_via: "rsync" roles: - ansistrano.deploy See  https://github.com/ansistrano/deploy for the vars to customize as needed. Run the playbook.

In this post, I am going to run a sample Spring application, which was created at:  REST with Spring: Quick Start  . Assuming that you have the jar file at: ./build/libs/rest-service-0.0.1-SNAPSHOT.jar Prepare Docker Files % vim Dockerfile FROM arm64v8/openjdk ADD ./build/libs/rest-service-0.0.1-SNAPSHOT.jar greeting.jar CMD java -jar greeting.jar Note: arm64v8/openjdk is for M1 Chip. This solved the following build error: "The requested image's platform (linux/amd64) does not match the detected host platform (linux/arm64/v8)" % vim docker-compose.yml version: "3.9" services: web: build: . ports: - "80:8080" Build & Run % docker-compose up --build % curl http://localhost/greeting {"id":1,"content":"Hello, World!"}

In this post, I am going to run a Nginx example on Minikube in two ways: 1. declarative: kubectl apply -f [yaml] 2. imperative: kubectl create & expose declarative: kubectl apply -f [yaml] With a declarative way, you can define the resources as yamls and apply them. This is preferable in a long run, but could be tedious if you just want to run it as a test. % cat deploy.yaml apiVersion: apps/v1 kind: Deployment metadata:   labels:     app: nginx   name: nginx spec:   replicas: 1   selector:     matchLabels:       app: nginx   template:     metadata:       labels:         app: nginx     spec:       containers:       - image: nginx         name: nginx % cat service.yaml apiVersion: v1 kind: Service metadata:   labels:     app: nginx   name: nginx spec:   ports:   - port: 80     protocol: TCP     targetPort: 80   selector:     app: nginx   type: NodePort % kubectl apply -f deploy.yaml % kubectl apply -f service.yaml open nginx % minikube service nginx ... | default   | nginx |       

This post shows examples of kubectx & kubens. install % brew install kubectx This will install both kubectx and kubens. kubectx kubectx help manage k8s contexts. % kubectx -h USAGE:   kubectx                       : list the contexts   kubectx <NAME>                : switch to context <NAME>   kubectx -                     : switch to the previous context   ... Listing the contexts is as simple as follows: % kubectl config get-contexts CURRENT   NAME        CLUSTER     AUTHINFO    NAMESPACE *         kind-kind   kind-kind   kind-kind              minikube    minikube    minikube    default % kubectx kind-kind minikube Change the context: % kubectx minikube Switched to context "minikube". % kubectx          kind-kind minikube % kubectx - Switched to context "kind-kind". % kubectx   kind-kind minikube kubens kubens help manage k8s namaepaces (ns). % kubens -h      USAGE:   kubens                    : list the namespaces in the current context   kubens

In this post, I am going to try Minikube on Mac with M1 Chip. what is minikube Minikube is k8s tool running on a local machine. See also kind  for multi cluster implementation for local k8s. install % curl -LO https://storage.googleapis.com/minikube/releases/latest/minikube-darwin-arm64 % install minikube-darwin-arm64 /usr/local/bin/minikube % minikube version  minikube version: v1.20.0  Note: Installing with brew fails due to a different binary as of 2021-05-24. % brew install minikube % minikube version ❌  Exiting due to MK_WRONG_BINARY_M1: You are trying to run amd64 binary on M1 system. Please use darwin/arm64 binary instead (Download at https://github.com/kubernetes/minikube/releases/download/v1.20.0/minikube-darwin-amd64.) % brew uninstall minikube start The default driver 'virtualbox' is not supported on M1, but you can use 'docker' driver:  https://minikube.sigs.k8s.io/docs/drivers/docker/  . Make sure docker is running, and then specify the driver when starting

HashMap is the hash table implementation in Java. Check  this post  for time complexity. https://docs.oracle.com/javase/8/docs/api/java/util/HashMap.html The methods include: V put(K key, V value) boolean containsKey(Object key) V get(Object key) V remove(Object key) Set<K> keySet() etc Example import java.util.HashMap; import java.util.Map; public class HashMapExample {   public static void main(String[] args ) {     Map<String, Integer> map = new HashMap<String, Integer>();     map .put( "a" , 1);     map .put( "b" , 2);     map .put( "c" , 3);     System. out .println( map .get( "a" )); // 1     System. out .println( map .get( "z" )); // null     if ( map .containsKey( "b" )) {       System. out .println( map .get( "b" )); // 2     }     for (String key : map .keySet()) {       int val = map .get( key );       System. out .println( val ); // 1, 2, 3 (in undefined order)