Docker tagging using REST API

Adding additional tags to the image will be a common process in the CICD world, the additional tags would be something like the build number, test result, etc.,

When adding multiple tags it will be very heavy if we are doing the tagging locally and then pushing the tagged image to the server. So instead of doing like that, we can use the docker HTTP REST API which will be lighting fast tagging and will add the tag to the remote docker repository

Below is the example of tagging an image in a remote repository using python

def addAssociatedTag(imageName, tag, associatedTag, bearerToken):
    header = {'Authorization': ''}
    header['Authorization'] = 'Bearer ' + bearerToken
    header['Accept'] = 'application/vnd.docker.distribution.manifest.v2+json'
    res = requests.get(
            url="https://docker.io/v2/" + imageName + "/manifests/" + tag,
            headers=header)
    print('Retrieved the metifests status is ' + str(res.status_code))   
    # Add the associated tag by passing the same manifests
    header['Accept'] = '*'
    res = requests.request(
            "PUT",
            url="https://docker.io/v2/" + imageName + "/manifests/" + associatedTag,
            headers=header,
            data=res.content)      
    response_status = res.status_code
    print('Adding associated tag for ' + imageName + ':' + tag + ' with ' + imageName + ':' + associatedTag + ' is = ' + str(response_status))
    return response_status

In the above, the setting the 'Accept' header is very important while getting the manifests. If we do not set it to 'application/vnd.docker.distribution.manifest.v2+json'then we will have the default 'application/json' which will not be correct when we use the content for adding the associated tags and we will get below error

{
    "errors": [
        {
            "code": "MANIFEST_LAYER_UNKNOWN",
            "message": "blob unknown to registry",
            "detail": {
                "digest": "sha256:a3ed95caeb02ffe68cdd9fd84406680ae93d633cb16422d00e8a7c22955b46d4"
            }
        }
    ]
}

Details about other docker REST APIs are in https://github.com/venkatesh-mohanram/continuous-learning/blob/master/docker/httpapiv2.md

To know a Docker image exists with REST API

 Most of the time when it comes to docker, we play with using the CLI with 'docker' command. If we want to pull an image, tag an image, push an image we do all that with CLI only. However, apart from CLI, the docker repository supports varieties of REST API to do plenty of things and here I am planning to cover a few things like below

Manifest resource

The manifest rest resource can be used in a way how we want, for eg: if we want to know whether the image exists with a given tag then we can use the GET method of it

def checkAlreadyPresent(imageName, tag, bearerToken):
    auth_header = {'Authorization': ''}
    auth_header['Authorization'] = 'Bearer ' + bearerToken
    res = requests.get(
            url="https://docker.io/v2/" + imageName + "/manifests/" + tag,
            headers=auth_header)
    return res.status_code

You can also refer to

https://github.com/venkatesh-mohanram/continuous-learning/blob/master/docker/httpapiv2.md

mvn dependency:tree - rescuer during build issues

Maven is one of the very good build tools and is still popular among many users. Even though we use it for a long time, we use to remember or use only a limited number of its commands like 'mvn clean install', 'mvn package', mvn test' etc

we get to know many of its commands only when we face issues, one of the nice command is the 'mvn dependency:tree' to get all the dependencies including the transitive dependencies we have. In this blog, I am going to talk about this particular command

We should execute the below command from the folder where we have the pom.xml file

$ mvn dependency:tree

This will print all the dependencies from the root till the last jar, this will help to identify what are the transitive dependencies that we have.

We have varieties of options to fix the transitive deps error, 

1. Add the transitive dependency into <exclusions> list

If you have control over the dependency then you can do one of the following

2.  make the transitive deps in the provided scope https://maven.apache.org/guides/introduction/introduction-to-dependency-mechanism.html#Dependency_Scope