create an application instance in Public network from custom image

Custom Image

In Oracle Cloud Infrastructure (OCI), a custom image is a reusable template of a compute instance that includes your operating system, configurations, patches, and installed software. Its importance lies in ensuring consistency, security, and efficiency when deploying multiple servers across your cloud environment.

🖥️ What is a Custom Image in OCI?

• A custom image is a snapshot of a compute instance that you create in OCI.

• It captures:

Operating system state (Linux, Windows, etc.)

Installed applications and patches

Configuration settings (network, security, packages)

• Once created, you can use this image to launch new instances that are identical to the original.

🔑 Importance of Custom Images in OCI

1. Consistency Across Deployments

• Every new instance launched from the custom image has the same OS, software, and security settings.

• Eliminates manual configuration errors and ensures uniformity across environments (dev, test, prod).

2. Security & Compliance

• Hardened images can be created with security patches and compliance settings already applied.

• Ensures all future servers meet organizational or regulatory standards (e.g., PCI-DSS, HIPAA).

3. Efficiency & Speed

• Saves time by avoiding repetitive installation and configuration steps.

• Ideal for scaling applications quickly in OCI regions.

4. Disaster Recovery & Backup

• Custom images act as a backup of a known-good state.

• In case of failure, you can redeploy servers from the image without rebuilding from scratch.

5. Portability

• Custom images can be exported and imported across regions or even tenants in OCI.

• Useful for global deployments where identical environments are needed in multiple locations.

🛠️ Steps to Create a Custom Image

1. Prepare the Instance

first we login into our existing instance via putty application

Now we install all required security application/software in to our server

1. Install Telnet

yum install telnet

2. Intall httpd

sudo dnf install httpd -y

3. Install Unzip

yum install unzip

4. Install Curl

yum install curl

5. Check Status of firwalld

systemctl status firewalld

Before Start Create Custom image we will check the installed application/software list

yum list installed

by use this command we will get all installed software/application list running in our server.

if we want to check specific software/application so we will use its unic name in command and get the result.

yum list installed curl telnet httpd unzip firewalld

Ones we confirm all the required software/application installed in our server so we will process for the next step.

2.Create Custom Image in oci Consol

Navigate to Burger menu - compute - instances - click on current instance [bastion_source_server_a] - click on action - More actions - Clicl on Create Custom Image

Now give the name for custom image and click on create image

We can see our created image in Custom Image option

Custom image created succesfully. Now its ready for instance creation.

3. Create Instance using custom image

In Image and shape click on change image option and select Myimages

Now select the custom image and click on select image

After select custom image do all process as per process and create the instance.

New Instance Successfully created with custom image.

Now we Login into the new server using putty application and check the installed application/software list

yum list installed curl telnet httpd unzip firewalld

Here we see that all required applicaiton/software already available here and we do not need to install it manually.