Wayne 9:51 pm on July 10, 2019

Install

apt-get update
apt-get install docker.io sudo usermod -a -G docker $USER 
systemctl start docker
systemctl enable docker

then make a logoff , use groups to check you are in docker group or not:

groups

build image:

create a Dockerfile file and then run

docker build -t your_image .

list images and containers

docker images docker images-l

docker container ls --all

run a container and check the port:

docker run -d -p 8800:80 --name your_container your_image
docker port your_container

detached run the image as a container and map the 8800 port of the container to host 80 port

Then we can check that the new container with name based on ‘nginx_image’ is running, List the running containers:

docker ps

Or check all containers

docker ps -a
docker stop your_container
docker rm your_container
docker rmi your_image

Pull an image from a registry

docker pull alpine:3.4

Retag a local image with a new image name and tag

docker tag alpine:3.4 myrepo/myalpine:3.4

docker login my.registry.com:8000

Push an image to a registry

docker push myrepo/myalpine:3.4

Stop a running container through SIGTERM

docker stop my_container

Stop a running container through SIGKILL

docker kill my_container

Create an overlay network and specify a subnet

docker network create --subnet 10.1.0.0/24 --gateway 10.1.0.1 -d overlay mynet

List the networks

docker network ls

Delete all running and stopped containers

docker container prune Or this command in old versions: docker rm -f $(docker ps -aq)

 docker rm 305297d7a235 ff0a5c3750b9

Create a new bash process inside the container and connect it to the terminal

docker exec -it my_container bash

Print the last 100 lines of a container’s logs

docker logs --tail 100 my_container

docker run – Runs a command in a new container.
```
docker run hello-world
docker run -it busybox sh
```
docker start – Starts one or more stopped containers
docker stop – Stops one or more running containers
docker build – Builds an image form a Docker file
docker pull – Pulls an image or a repository from a registry

docker pull busybox

docker pull ubuntu:16.04

docker push – Pushes an image or a repository to a registry
docker export – Exports a container’s filesystem as a tar archive
docker exec – Runs a command in a run-time container
docker search – Searches the Docker Hub for images
```
docker search elasticsearch
docker search mysql
```
docker attach – Attaches to a running container
docker commit – Creates a new image from a container’s changes
Watch the log

docker container logs my_container

Spring boot build version and time access

Spring boot can create the build version info for you automatically and with a default bean to access these information. I found this link is very helpful on this and i jus tlist main points at here.

https://www.vojtechruzicka.com/spring-boot-version/

build-info goal create the version info

<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<executions>
<execution>
<goals>
<goal>build-info</goal>
</goals>
</execution>
</executions>
</plugin>

2. In java code, just use BuildProperties to get the version info. You cna then display on UI and logs.

@Autowired
BuildProperties buildProperties;

3. you can even add more properties in POM to let it saved in build-info, you can refer to the link details for this.

Wayne 12:46 am on February 8, 2019

How to let swagger control group display

In Swagger, you normally divide the API into groups and each group will have a Docket.

But many times, you do not want someone or some environment to see all groups . you want to control each group showing or not. This looks like a difficult task after some search. But in fact swagger already has this feature in Docket.

@Bean
public Docket myDocket() {
return new Docket(DocumentationType.SWAGGER_2).groupName("MYAPI").apiInfo(...).select().paths(....)
.build().useDefaultResponseMessages(false).forCodeGeneration(true).enable(true);
}

So enable(boolean) is part to control enable method for the group. You can use your configuration or role logic to control this flag value to control the group here.

Wayne 12:39 am on February 8, 2019

How to let your spring boot pick up external property file

You may already see that ./config/application.properties can override the default spring boot application.properties settings. But when you deploy your app to tomcat and with many other web app together, then you need to have unique properties files foe each app and also make external property file be picked up by web app.

So let us do something like this:

Change in your java main code to let your app use a unique properties file instead of application.properties.

@SpringBootApplication
public class MyApplication {

    public static void main(String[] args) {
        System.setProperty("spring.config.name", "myapp");
        SpringApplication.run(MyApplication.class, args);
    }
}

For war version of tomcat:

public class ServletInitializer extends SpringBootServletInitializer {

    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder application) {
        return application.sources(MyApplication.class).properties("spring.config.name: myapp");
    }

}

Then name your properties file like: myapp.properties, instead of the default name.

2. Now let us also enable the external property file to override the default myapp.properties.

in Spring boot, it is just ./config/myapp.properties

For tomcat version, we need to add env variable to do this. Set a spring_config_location environment variable pointing to the folder that contains your myapp.properties file. In the case of Tomcat you can do this by adding the following line to your <TOMCAT_HOME>/bin/setenv.sh file (create the file if missing):

export spring_config_location=<TOMCAT_HOME>/conf/

Place the myapp.properties properties file in that folder <TOMCAT_HOME>/conf/.

So every app will looking into the conf folder to look for their unique properties file to load.

Refer to:

https://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-external-config.html

Wayne 9:53 pm on February 7, 2019

Java native memory tools and usage related

https://dzone.com/articles/java-memory-and-cpu-monitoring-tools-and-technique

https://www.ibm.com/developerworks/library/j-nativememory-aix/

https://stackoverflow.com/questions/12797560/command-line-tool-to-find-java-heap-size-and-memory-used-linux

https://dzone.com/articles/java-memory-and-cpu-monitoring-tools-and-technique

https://stackoverflow.com/questions/2756798/java-native-memory-usage




java -XX:+PrintFlagsFinal -version | grep -iE 'HeapSize|PermSize|ThreadStackSize'

Wayne 1:26 am on February 7, 2019

Issue: An irrecoverable stack overflow has occurred.

Issue:

An irrecoverable stack overflow has occurred. Please check if any of your loaded .so files has enabled executable stack (see man page execstack(8))

Reason:

This issue happens when I call a c++ So lib from java by JNA. This mostly caused by input a big chunk of data into the function interface of the C++ function. There is a limit of the Thread Stack Size defined for java’s thread. Normally is 512K-1024K.

And by change the Xss size you could change the stack size. but you should be careful on this when you have many threads need to open.

Refer http://xmlandmore.blogspot.com/2014/09/jdk-8-thread-stack-size-tuning.html