Tag Archives: OCI

Looking inside Container Images

Containers & Kubernetes, Networking & SDN, , , , ,

This blog is a continuation of my previous blog on Container standards. In this blog, we will look inside a Container image to understand the filesystem and manifest files that describes the Container. We will cover Container images in Docker, APPC and OCI formats. As mentioned in previous blog, these Container images will converge into OCI format in the long run.

I have picked two Containers for this blog: “nginx”which is a standard webserver and “smakam/hellocounter” which is a Python web application.

Docker format:

To see Container content in Docker format, do the following:

docker save nginx > nginx.tar
tar -xvf nginx.tar

Following files are present:

  • manifest.json – Describes filesystem layers and name of json file that has the Container properties.
  • <id>.json – Container properties
  • <layer directory> – Each “layerid” directory contains json file describing layer property and filesystem associated with that layer. Docker stores Container images as layers to optimize storage space by reusing layers across images.

Following are some important Container properties that we can see in the JSON file:

Continue reading Looking inside Container Images →

Container Standards

Containers & Kubernetes, Networking & SDN, , , , , , ,

In this blog, I will cover some of the standardization effort that is happening in the Containers area. I will cover some history, current status and also mention how the future looks like. In the next blog, we will look inside ACI and OCI Container images.

Container Standards

Lot of developments in Container area are done as Open source projects. That still does not automatically mean that these projects will become standards. Following are the areas where Container standardization is important:

  • Container image format – Describes how an application is packaged into a Container. The application can be an executable from any programming language. As you would know, Containers packages an application along with all its application dependencies.
  • Container runtime – Describes the environment(namespaces, cgroups etc) necessary to run the Container and the APIs that Container runtime should support.
  • Image signing – Describes how to create Container image digest and to sign these so that Container images can be trusted.
  • Image discovery – Describes alternate approaches to discover Container images other than using registry.
  • Container Networking – This is a pretty complex area and it describes ways to network Containers in same host and across hosts. There are different implementations based on the use-case.

Having common Container standards would allow things like this:

Continue reading Container Standards →