Sailing Towards Standardization: Open Container Initiative (OCI) Explained

Oct 13, 2023 by Sameer Kulkarni
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Sailing Towards Standardization: Open Container Initiative (OCI) Explained

Being a software developer in the 21st century is a boon with so many tools to assist us. From AI-assisted code editors to automated build and deploy tools, life is much simpler. Back in the day, developers built & tested applications on their own machines. This led to “But It works on my machine” issues.

Deploying applications wasn’t easy as it was all about manually installing the dependencies and configuring the application on multiple servers. This process was not only slow but prone to errors. This was a major hindrance when it came to building and shipping applications faster.

Fortunately, Containers was the answer to the above shortcomings. Containers were game changers as they were portable and provided a consistent environment for applications. Today containers are everywhere. At Acorn, they enable our entire platform and make it possible to deploy applications.

In this post, we will discuss containers and the Open Container Initiative (OCI) that was set up to keep containers together and make their use easier.

The Need For Containers

The introduction of containers in the early 2000s was a pivotal point in the way we developed and deployed applications. Though it wasn’t mainstream until Docker was released in 2013. Until then, developers struggled with misconfigurations, missing dependencies, and environment drift between dev and prod leading to time-consuming debugging and deployments.

Containers changed these by encapsulating the applications and their dependencies in a single, self-contained unit. This ensured a consistent and reliable behavior of applications in different environments. These containers were lightweight and fast thus making them portable and scalable.

Everyone was fast to realize the benefits of containers and hence, everyone started building one. And there were containers all over the place, that’s when the need for a tool like Kubernetes came in. The number of containers wasn’t a real challenge, but the lack of uniformity and standardization was.

With everyone building their own container, there were compatibility issues and vendor lock-in risks. Moreover, it was challenging to manage and execute containers across different runtimes and platforms. Recognizing the need for standardization, the Open Container Initiative (OCI) was born.

Understanding Open Container Initiative (OCI)

Started in 2015, the Open Container Initiative is a collaborative project within the Linux Foundation with an aim to establish open industry standards for containers and runtimes. The primary objective of OCI was to create open, vendor-neutral specifications that promote interoperability, portability, and compatibility among different container runtime environments and platforms. Technology companies like Google, RedHat, Microsoft and Docker collaborated to form the OCI.


Objectives of OCI

Standard Container Format

The foremost objective was to create a standard container format known as OCI Image Specification. This defines the structure and layout of container images, along with how they should be built, distributed, and stored. By adhering to this standard specification, developers are able to create container images that can be executed on various container runtimes without the need for any modification.

Standard Container Runtime

The next objective was to establish a standard container runtime environment known as OCI Runtime Specification. This defines how the runtimes should execute the containers alongside listing details of how the container image and host OS should communicate. Standardizing the runtime environment ensures that applications behave consistently regardless of the underlying platform or infrastructure.

Compatibility and Portability

Both Container Format and Runtime ensure compatibility and portability. By adhering to the OCI standards, developers can easily move their containerized applications from one container runtime to another across different cloud platforms while being guaranteed a consistent environment. The compatibility ensures there’s no vendor-lock-in which makes porting easier.

Open Governance

The open governance framework of OCI ensures that everyone including a container runtime developer, cloud developers, and end-users actively participate in the development and evolution of OCI specifications. This leads to transparency and collaboration between different stakeholders which helps address the real-world needs faster.

OCI Specifications

OCI specifications are means to allow container runtimes and platforms to ensure compatibility and portability, allowing containers to be executed consistently across various environments. Let us look at some aspects of each of the specifications

OCI Image Specification

  • Manifest File: The specification mandates a manifest file that describes the image configuration and a set of layers required to build it. This helps the runtime understand how to build and execute the image.
  • Layer Format: Specifies a standard format for container image layers that ensures that container images can be shared and executed across different platforms and runtimes.
  • Configuration File: This file lists the container’s configuration like environment variables, entry point, working directory, etc.
  • Image Layout: This defines the directory structure and layout of a container image, ensuring consistency and ease of use with various tools and runtimes. You can read the full list of OCI Image Specifications to learn more.

OCI Runtime Specification

  • Runtime Bundle: A runtime bundle has all the required information and files to execute a container. This bundle contains the container’s root file system, configuration files, and other essential components.
  • Runtime Configuration: This defines the runtime configurations that include the parameters for container processes, such as process ID, namespace capabilities, and resource configurations.
  • Resource Management Configuration: Provides guidelines for resource and device management within the container. Guidelines around cgroups and CPU/Memory limits are provided here.
  • Lifecycle Hooks: The specification also introduces Lifecycle hooks that allow users to execute custom actions before or after a container is created or destroyed. You can read the full list of OCI Runtime Specifications to learn more.

Why Should You Make Your Containers OCI-Compliant?

In the rapidly evolving container landscape, ensuring your containers are OCI-Compliant is the key to unleashing their true potential. Let us show you the transformative benefits you get when your containers are OCI-compliant.

Interoperability and Portability

OCI compliance ensures that your container images are built to a standardized format that major container runtimes, like Docker and containerd. This guarantees interoperability and allows your containers to run consistently across various container runtimes without any modification. You can also effortlessly move your containers between different environments, from local development to cloud deployment, with minimal friction.

Vendor-neutral and future-proofing

Building OCI-compliant containers protect your applications from being tied to a specific container runtime or platform. With OCI-compliant containers, you have the freedom to choose the most suitable container runtime or cloud provider for your needs without facing disruptive migrations. This flexibility ensures that your containers remain adaptable to changes in the container landscape and future technology advancements.

Broader Ecosystem Support

There’s a thriving container ecosystem supported by a diverse community of developers, container runtime maintainers, cloud providers, and other stakeholders that you get access to when you build OCI-compliant containers. By making your containers OCI-compliant, you contribute to the growth and improvement of the container ecosystem. This collaboration fosters knowledge sharing, shared learnings, and continuous improvements driven by the community’s collective experiences and expertise.


It’s been just over a decade since containers have been around, but it seems like they’ve been around forever. The container landscape is only going to grow from here. As per a recent CNCF survey, 44% of respondents are already using containers for nearly all applications and this number is only going to increase in the times to come.

To add to it, the widespread adoption of OCI standards just reiterates its importance in the container ecosystem. Embracing OCI compliance has become imperative as more and more businesses today recognize the value of interoperability, portability, vendor neutrality, and open governance.

OCI compliance empowers organizations to build, share, and deploy containerized applications with confidence, paving the way for a more connected, efficient, and thriving container ecosystem.

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