Upload a tarball image to Docker hub with Skopeo

Let’s create a tar of a docker image (for example, busybox:latest) in a tarball archive:

docker save busybox:latest  -o test-bb.tar

Then login into your docker hub repository directly with Skopeo:

skopeo login docker.io

Assuming that the test-alpine.tar file is in the same directory when you are executing the command, to upload it to your docker hub, you simply have to run:

skopeo copy docker-archive:./test-bb.tar docker://lauraliparulo/busylaura:latest

In my case I had to execute the command as root:

If you do it correctly, you should see the tag added to your docker hub repository:

It’s super easy!

No more Minishift? Let’s install Openshift Local 4.X

It seems like Minishift has been discontinued. Starting from Openshift 4.X you can alternatively use Openshift Local to set up your cluster and get started.

Once you login in into your Redhat account, you can install a local version of Openshift, by following the instructions at:

https://console.redhat.com/openshift/create/local

Follow the step 1: downlaod both the Openshift local archive and the pull secret (text file).

The latest version available for Openshift Local is currently 2.20:

https://access.redhat.com/documentation/en-us/red_hat_openshift_local/2.20/html/getting_started_guide/index

With Openshift Local you get an ephemeral cluster for learning and development purpose, with no upgrade opportunity.

It’s basically a single node platform, where the node works both as control plane and worker node.

Cluster monitoring is disabled, so you can’t use the web console to the full.

The Openshift local cluster we are using is also known as CodeReadyContainers (CRC). It’s basically a minimal environment for development and testing purposes.

To install the CRC environment on ubuntu, you can follow the steps similiar to the old Minishift installation:

https://dsri.maastrichtuniversity.nl/docs/guide-local-install/

Then you need to extract the crc binary from the Openshift local version installed and put int under /usr/bin.

This will allow you to run crc commands from the bash shell.

Run “crc setup”. you will get an output like:

CRC is constantly improving and we would like to know more about usage (more details at https://developers.redhat.com/article/tool-data-collection)
Your preference can be changed manually if desired using 'crc config set consent-telemetry <yes/no>'
Would you like to contribute anonymous usage statistics? [y/N]: y
Thanks for helping us! You can disable telemetry with the command 'crc config set consent-telemetry no'.
INFO Using bundle path /home/laura/.crc/cache/crc_libvirt_4.13.0_amd64.crcbundle 
INFO Checking if running as non-root              
INFO Checking if running inside WSL2              
INFO Checking if crc-admin-helper executable is cached 
INFO Caching crc-admin-helper executable          
INFO Using root access: Changing ownership of /home/laura/.crc/bin/crc-admin-helper-linux 
INFO Using root access: Setting suid for /home/laura/.crc/bin/crc-admin-helper-linux 
INFO Checking if running on a supported CPU architecture 
INFO Checking if crc executable symlink exists    
INFO Creating symlink for crc executable          
INFO Checking minimum RAM requirements            
INFO Checking if Virtualization is enabled        
INFO Checking if KVM is enabled                   
INFO Checking if libvirt is installed             
INFO Checking if user is part of libvirt group    
INFO Checking if active user/process is currently part of the libvirt group 
You need to logout, re-login, and run crc setup again before the user is effectively a member of the 'libvirt' group.

Restart your machine and retry “crc setup”. This time it will download the bundle:

Downloading bundle: /home/laura/.crc/cache/crc_libvirt_4.13.0_amd64.crcbundle…

At the end, you should get something like:

Your system is correctly setup for using CRC. Use ‘crc start’ to start the instance
The you can finally run “crc start -p pull-secrets.txt”.

It will ask to enter the pull secret, that you downloaded previousyl from https://console.redhat.com/openshift/create/local.

The crc utility will install the user’s pull secret to the instance disk.

It will create a virtual machine for Openshift 4.x.x. and finally start the openshift instance.

It will take 5-10 minutes if you have more than 64 GB ram… So relax and wait for the following messages, if everything works correctly:

Started the OpenShift cluster.

The server is accessible via web console at:
  https://console-openshift-console.apps-crc.testing

Log in as administrator:
  Username: kubeadmin
  Password: xxxxxxxxxxxxxxxxx

Log in as user:
  Username: developer
  Password: developer

Use the 'oc' command line interface:
  $ eval $(crc oc-env)
  $ oc login -u developer https://api.crc.testing:6443

You will be able to access the instance in the browser and login.

You can download the OC CLI directly from the web console. Extract the binary and move it to your binary folder:

sudo mv oc /usr/local/bin/

You can try to login via CLI:
> oc login -u developer https://api.crc.testing:6443

If you login with the admin credentials, of course you have access to more information.

If it fails to restart:

crc stop
crc delete -f

crc cleanup
sudo systemctl restart libvirtd.service
crc start

The defaul created services are of type ClusterIP, but you can easily convert them to NodePort:

oc patch svc hello-world-go-openshift-git -p '{"spec": {"type": "NodePort"}}'

To expose:
kubectl expose pod rabbitmq-0 --port=15672 --target-port=15672 --type=NodePort

Spring – security context management

Once the Authentication Filter intercept the authentication request, the details about the user that has been authenticated are stored in the security context.

The security context represent the instance storing the Authentication Object, that is been later accessed by the Controllers.

The context is managed by a SecurityContextHolder, with one of the following three strategies:

  • MODE_THREADLOCAL – each request has its on thread (own sec. context)
  • MODE_INHERITABLETHREADLOCAL – security context copied to next thread (@Async methods inheriting the context)
  • MODE_GLOBAL – same context for all the threads (not thread safe!)

You can get the authentication object from the SecurityContextHolder:

SecurityContext context = SecurityContextHolder.getContext();
  Authentication a = context.getAuthentication();

If you want to specify a different strategy than threadlocal, you have to set the strategy in the configuration, for example:

@Configuration
@EnableAsync
public class SecurityConfig{

//other lines of code

  @Bean
  public InitializingBean initializeSecurityContextHolder() {
    return () -> SecurityContextHolder.setStrategyName(
      SecurityContextHolder.MODE_INHERITABLETHREADLOCAL);
  }
}

If the new threads are not created by the Spring framework, you need to implement the security context propagation to the new thread on your own.

To solve the issue you can use a DelegatingSecurityContextRunnable or DelegatingSecurityContextCallable, if you need to return a value, to copy the context to the next thread “manually”.

Instead of simply using an ExecutorService, you can use its decorator provided by Spring security, called “DelegatingSecurityContextExecutorService “to propagate the thread:

@GetMapping("/hello")
public String hello() throws Exception {
  Callable<String> task = () -> {
    SecurityContext context = SecurityContextHolder.getContext();
    return context.getAuthentication().getName();
  };

  ExecutorService e = Executors.newCachedThreadPool();
  e = new DelegatingSecurityContextExecutorService(e);
  try {
    return "HEllo, " + e.submit(task).get() + "!";
  } finally {
    e.shutdown();
  }
}

Spring security – Password encoding delegation

The AuthenticatioProvider, that implements the authentication logic, requires a Password Encoder bean to validate the password propertly.

PasswordEncoder is the contract (interface) provided by Spring for this purpose.

You can treat passwords as plain text with NoOpPasswordEncoder, or choose an algorithm (like BCrypt, Argon2, etc-). Of course you do want make harder to read and steal passwords, so you need a definitely need the encoding!

If you want to allow to use different kinds of encoding algorithms , you can use the DelegatingPasswordEcoder.

The PasswordEncoderFactories method called “createDelegatingPasswordEncoder” will help you keeping your bean configuration more generic, by providing a Map of all the encoders:

@Bean
PasswordEncoder passwordEncoder(){
      return PasswordEncoderFactories.createDelegatingPasswordEncoder();
}

If you look into the factory method, you see that the default is Bcrypt, but you can use any other algorithm:

	public static PasswordEncoder createDelegatingPasswordEncoder() {
		String encodingId = "bcrypt";
		Map<String, PasswordEncoder> encoders = new HashMap<>();
		encoders.put(encodingId, new BCryptPasswordEncoder());
		encoders.put("ldap", new org.springframework.security.crypto.password.LdapShaPasswordEncoder());
		encoders.put("MD4", new org.springframework.security.crypto.password.Md4PasswordEncoder());
		encoders.put("MD5", new org.springframework.security.crypto.password.MessageDigestPasswordEncoder("MD5"));
		encoders.put("noop", org.springframework.security.crypto.password.NoOpPasswordEncoder.getInstance());
		encoders.put("pbkdf2", new Pbkdf2PasswordEncoder());
		encoders.put("scrypt", new SCryptPasswordEncoder());
		encoders.put("SHA-1", new org.springframework.security.crypto.password.MessageDigestPasswordEncoder("SHA-1"));
		encoders.put("SHA-256", new org.springframework.security.crypto.password.MessageDigestPasswordEncoder("SHA-256"));
		encoders.put("sha256", new org.springframework.security.crypto.password.StandardPasswordEncoder());
		encoders.put("argon2", new Argon2PasswordEncoder());

		return new DelegatingPasswordEncoder(encodingId, encoders);
	}

This will allow you to use several encoding algorithms:

    @Override
    protected void configure(AuthenticationManagerBuilder auth) throws Exception {
        auth.inMemoryAuthentication()
                .withUser("admin")
                .password("{bcrypt}$2a$10$7tYAvVL2/KwcQTcQywHIleKueg4ZK7y7d44hKyngjTwHCDlesxdla")
                .roles("ADMIN")
                .and()
                .withUser("laura")
                .password("{sha256}1296cefceb47413d3fb91ac7586a4625c33937b4d3109f5a4dd96c79c46193a029db713b96006ded")
                .roles("USER");
    }

In order to make the DelegatingPasswordEncoder recognize the algorithm (for example Bcrypt), you need to add a string like "{bcrypt}" as prefix, as you can see in the example above.

Spring – search through entities with ExampleMatchers

In the *.data.domain package in Spring you can find useful classes to search through the database (if you are using the JPA repository interface) rather quickly.

The Example and ExampleMatcher class will do the trick.

For example, if you’re looking for albums in a Table:

  public List<Album> search(AlbumSearchDTO search) {
      Album probe = new Album();
        if (StringUtils.hasText(search.value())) {
          probe.setTitle(search.value());
          probe.setArtist(search.value());
          probe.setDescription(search.value());
        }
        Example<Album> example = Example.of(probe, //
          ExampleMatcher.matchingAny() //
            .withIgnoreCase() //
            .withStringMatcher(StringMatcher.CONTAINING));
        return repository.findAll(example);
      }

You can pass the Example collection to a findAll method directly, and it will return a subset of rows containing the string …anywhere on the columns.

Check it out!

Spring Database Repository interfaces…

Spring offers you more than a way to get your database access operations easily ready out of the box.

You can find interfaces to extends to create your repository in two packages:

  • org.springframework.data.repository
  • org.springframework.data.jpa.repository

In the latter package you can the JPA specific extension of the Repository interface defined in org.springframework.data.repository:

https://docs.spring.io/spring-data/data-jpa/docs/current/api/org/springframework/data/jpa/repository/JpaRepository.html

You can simply create a Repository object as an interface, like:

public interface UserAccountRepository extends Repository<UserAccount,Long>{}

Or you can use a more specific one like:

CrudRepository<T,ID>Interface for generic CRUD operations on a repository for a specific type
ListCrudRepository<T,ID>Interface for generic CRUD operations on a repository for a specific type.
ListPagingAndSortingRepository<T,ID>Repository fragment to provide methods to retrieve entities using the pagination and sorting abstraction.
PagingAndSortingRepository<T,ID>Repository fragment to provide methods to retrieve entities using the pagination and sorting abstraction.
JpaRepository<T,ID>JPA specific extension of Repository.

You can extend one of them or more together according to your needs.

Tje JPARepository interface extends the CrudRepository and provides you with additional methods, like findAll, saveAndFlush, etc.

.

Setting up Node and npm packages with frontend-maven-plugin

An extraordinary way to get your nodejs, npm and all packages installed and running without any worries is provided by a maven plugin called “frontend-maven-plugin”.

In your pom.xml section, you need to add the plugin and its goal in the build section:

<build>
		<plugins>

			<plugin>
				...
			</plugin>

			<plugin>
				<groupId>com.github.eirslett</groupId>
				<artifactId>frontend-maven-plugin</artifactId>
				<version>1.12.1</version>

				<executions>

					<execution>
						<goals>
							<goal>install-node-and-npm</goal>
						</goals>
						<phase>generate-resources</phase>
					</execution>

					<execution>
						<id>npm install</id>
						<goals>
							<goal>npm</goal>
						</goals>
						<phase>generate-resources</phase>
						<configuration>
							<arguments>install</arguments>
						</configuration>
					</execution>

         		  <execution>
                    <id>npm run-script build</id>
                    <goals>
                        <goal>npm</goal>
                    </goals>
                    <phase>generate-resources</phase>
                    <configuration>
                        <!-- arguments>run-script build</arguments-->
                    </configuration>
                </execution>

				</executions>

				<configuration>
					<nodeVersion>v16.14.2</nodeVersion>
				</configuration>

			</plugin>
		</plugins>
	</build>

Make sure your package.json file is in the root folder.

Then run:

mvn generate-resources

That’s it!

You can find a working example on my githup repo:

https://github.com/lauraliparulo/spring-rest-react-demo

Spring Data – Optimistic locking with @Version

Spring Data provides pessimistic locking as default locking mechanism.

It means that the database record gets locked exclusively until the operation completes. This approach might be prone to deadlocks and requires a direct connection to the database to be used indipendently.

Optimistic locking comes in play if you have a high-volume system and you don’t want to mantain a database connection for the whole session. This way the client doesn’t maintain a lock and you can use a different connection from a connection pool from time to time, each time you access the resource.

Optimistic locking can be achieved with timestamps or versioning

If you want to use it with Spring, you can use the @Version annotation and add an additional attribute in your entity or base entity class, like:

@MappedSuperclass 

public abstract class Person{

@Version

private Long version;

//other attribututes, getters and setters

   public Long getVersion() {

      return version;

   }

//add setter

}

In the database table you also need to specify the version column:

ALTER TABLE person ADD COLUMN version int NOT NULL DEFAULT 0;

If you execute PUT requests / update the table row, a consistency (and isolation) check will tell you if you are working on the newest version.

If your request has an older version, you will get an error (probably a 500 – internal server one)

Golang – commands with flag

Flag is a golang library to parse commands on the command line.

For example, let’s create an Hello World program that gets a name as parameter and returns the string:

package main

import (
	"flag"
	"fmt"
	"os"
)

func main() {

	name := flag.String("name", "", "The name to create the hello world message")
	flag.Parse()

	if *name == "" {
		fmt.Println("Enter your name:")
		flag.Usage()
		os.Exit(1)
	}

	fmt.Println("Hello,", *name)
}

Ton run the command and see the “Hello, Laura” message, assuming the file is called “flags.go”, run:

go run flags.go -name Laura

Golang – using Maps

Maps can be defined in Golang with the keywork map.

The type is defined in the square brackets, followed by the value:

For example:

package main

import "fmt"

func main() {

	//variable lenght arrays
	empty_map := map[string]string{}

	fmt.Println(empty_map)

	location_map := map[string]string{
		"city":    "Frankfurt",
		"state":   "Hessen",
		"country": "Germany",
	}

	fmt.Println(location_map)

	coordinates_map := map[string]float32{
		"latitude":  56.7,
		"longitude": 45.6,
	}

	fmt.Println(coordinates_map)

	//print specific values
	fmt.Println(coordinates_map["latitude"])
}
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