Jenkins Slave on AWS EC2 instances with SSH configuration

After configuring the  Jenkins Master we need to configure the slave or agent on EC2 instance. There are various methods to connect with the Slave node. In this post, 

I would like to share the SSH key-based remoting method.

Pre-requisites

• Jenkins Master already Up and Running
• Java (JDK) installed on the Slave node

Here we are in the slave machine and proceed with the following steps for configure a SSH based Jenkins slave.

How to create user and generate ssh-key on Slave?

Login to slave node terminal using ssh or PuTTY switch to root user. 

useradd jenkins_slave
mkdir -p /home/jenkins_slave
usermod -d /home/jenkins_slave jenkins_slave
tail -1 /etc/passwd # To check useradded to userlist

Now switch to the newly created user 'jenkins_slave'.

sudo su - jenkins_slave

SSH Key generate for 'jenkins_slave' user with the following command:

cd .ssh
ssh-keygen -t rsa -N ""

The above command will create two files in /home/jenkins_slave/.ssh folder id_rsa (private key) and id_rsa.pub (public key). Now navigate to the .ssh folder then push the public key content into authorized_keys file.

cat id_rsa.pub>authorized_keys

Now make the authorized_keys file permission to 700.

chmod 600 authorized_keys

How to Configure known_hosts on Master node?

Login to the "Master machine" and switch to user 'jenkins' and then create .ssh folder. Add the slave host to the known_hosts file using following command(ssh-keyscn).

cd .ssh;
ssh-keyscan -H 172.31.37.235>>known_hosts
chmod 600 known_hosts

All set on the master node about the slave node. Now go to the Jenkins dashboard. On the left pane select the "Manage Jenkins" > Manage Nodes and Cloud > New Node Enter the following values:

1. Name: node1
2. Description: Build server
3. # of executors: 5
4. Remote root directory: /tmp/slave 
5. Labels: node1
6. Usage: Use this node as much as possible
7. Launch method : Launch agents via SSH

a. Host: ip-address

b. Credentials: jenkins_slave

c. Host Key Verification Strategy: Known host file Verification Strategy

1. Availability: Keep this agent online as much as possible

Now go to the slave node and fetch the content of the id_rsa file (that is private key content).

In the Jenkins Dashboard  - On the left pane section select : Credentials 

Global Credentials(unrestricted)

Add Jenkins Global credentials

Scope: Global

Username : jenkins_slave (which was created in the above top step)

Private key copy the above content to the Jenkins Private key Text box from the slave node ~/.ssh/id_rsa

After configuring the slave settings, Save the Project. 

Finally, you can see the Node is active state as shown below:

Learn how to use git tag for Code Revisions

In this post, let's do an experiment with git tag command options. In GitOps we need to know what is a tag? How many types of git tags? We will learn about Creating, deleting, and listing tags for a project repository. Once everything is done, we need to know how to push the tag to the remote repository.

Work tree for git tag creation

Why git tagging?

1. Tagging is used to mark a commit stage as important
2. We can tag a commit for future references 
3. Typically tagging wiil be used to book mark release points in a Project.
4. Annotated tags will be recommend where you are working in team and collaborating for a project development.

Before you start on git tag

You must have a GitHub or GitLab account to work on a remote repository. Knowledge of basic repository creation on these Git clouds. On your git client shell (git bash as well) you must create the global user identity entries in the configurations.

[vagrant@mydev tags_handson]$ git config --list
user.email=bhavanishekhar@gmail.com
user.name=Pavan Devarakonda
core.repositoryformatversion=0
core.filemode=true
core.bare=false
core.logallrefupdates=true

# Now let's begin
 mkdir tags_handson
 cd tags_handson/
 git init
 echo "test1"> test1.txt

Enter some text into the test1.txt file.

What is git tag?

Git Tags are a simple aspect of the Git version control system, they allow you to identify specific release versions of your application code. You can think of a tag as a branch that doesn't change. Once the git tag is created, it loses the ability to change the history of commits.

Git supports two types of tags:

1. Annotated Tags: Annotated tags, however, are stored as full objects in the Git database.
2. Lightweight Tags: A lightweight tag is very much like a branch that doesn’t change — it's just a pointer to a specific commit.

How to Create tags in Git?

 To create a new tag execute the following command

Annotated tags store extra metadata such as Author name, Release notes, tag-message, and Date as full objects in the Git database. All this data is important for the public release of your project.

Tags can also include a more descriptive tag-message or annotation much like a commit message when you are about to merge. Usually, this is achieved by using (-a for annotation):

git tag -a v1.1 -m 'annotated tag test'

Lightweight tagging

It is simple to create and use, just need to pass the tag name example here for v1.0 the command:

git tag v1.0

How to delete the tags from the local and remote repo?

Unwanted tags we can remove from the repo using the -d or --delete option along with the git tag command. There are two levels of deletion could happens at local and remote

i. Delete a local tag

To remove both types of annotated and lightweight tag use the following git tag command with -d

git tag -d tag_name 

Example:

git tag -d v1.0

Note: If you try to delete a non existig Git tag, there will be the following error: 

git tag -d tag_name error: tag 'tag_name' not found. 

ii. Delete remote tags

To delete a tag from the remote git server with push tags

git push --delete origin remote_tag_name

Hope you are already global configuratoin with remote git server.

Example:

git push --delete origin v1.0.0-rc1

Listing tags 

To list-out all the tags in a work area, we can use

git tag 

Listing git tags
git tag -l '*rc*'

Now in this we can use regular expression in single quotes to see particular tags only, here I've selected all the tags with word contians 'rc'

Listing particular git tags

If you want to list all the tags in sorted order, that based on date :

git log --tags --simplify-by-decoration --pretty="%ai %d"

How to push tags? 

To push a single tag or a specific tag to remote repo:

git push origin v1.0 

To push all tag use following command:

git push origin --tags 

or
To push all the tags to remote (not recommended):

git push --tags 

Run this to push mytag to a project that is hosted on GitHub or GitLab on git origin

git push origin refs/tags/mytag

Best practice using the refs/tags instead of just specifying the . Why? It's recommended to use refs/tags since sometimes tags can have the same name as your branches and a simple git push will push the branch instead of the tag
To push annotated tags and current history chain tags use:

git push --follow-tags

This flag --follow-tags pushes both commits and only tags that are both:
Annotated tags (so you can skip local/temp build tags) Reachable tags (an ancestor) from the current branch (located on the history) 

You should only push annotated tags to the remote repo, and keep lightweight tags for local repo for development to avoid tag clashes. it won't push annotated tags on unrelated branches

Now...

In order to checkout a git tag , you would execute the following command
git checkout tags/tag-name -b branch-name eg as mentioned below.

 git checkout tags/v1.0 -b v1.0-branch 

To fetch the all tags use the command with git fetch:

git fetch --all --tags 

git tag cheat sheet

In my understanding about git tag is like branch but cannot move.

References: 

1. git cheat sheets
2. Stack overflow popular discussion about git tags
3. How do you push tags to Remote Repo