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kata-design-requirements.md

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Design requirements

The Kata Containers runtime MUST fulfill all of the following requirements:

OCI compatibility

The Kata Containers runtime MUST implement the OCI runtime specification and support all the OCI runtime operations.

runc CLI compatibility

In theory, being OCI compatible should be enough. In practice, the Kata Containers runtime should comply with the latest stable runc CLI. In particular, it MUST implement the following runc commands:

  • create
  • delete
  • exec
  • kill
  • list
  • pause
  • ps
  • start
  • state
  • version

The Kata Containers runtime MUST implement the following command line options:

  • --console-socket
  • --pid-file

CRI and Kubernetes support

The Kata Containers project MUST provide two interfaces for CRI shims to manage hardware virtualization based Kubernetes pods and containers:

  • An OCI and runc compatible command line interface, as described in the previous section. This interface is used by implementations such as CRI-O and containerd, for example.
  • A hardware virtualization runtime library API for CRI shims to consume and provide a more CRI native implementation. The frakti CRI shim is an example of such a consumer.

Multiple hardware architectures support

The Kata Containers runtime MUST NOT be architecture-specific. It should be able to support multiple hardware architectures and provide a modular and flexible design for adding support for additional ones.

Multiple hypervisor support

The Kata Containers runtime MUST NOT be tied to any specific hardware virtualization technology, hypervisor, or virtual machine monitor implementation. It should support multiple hypervisors and provide a pluggable and flexible design to add support for additional ones.

Nesting

The Kata Containers runtime MUST support nested virtualization environments.

Networking

  • The Kata Containers runtime MUST support CNI plugin.
  • The Kata Containers runtime MUST support both legacy and IPv6 networks.

I/O

Devices direct assignment

In order for containers to directly consume host hardware resources, the Kata Containers runtime MUST provide containers with secure pass through for generic devices such as GPUs, SRIOV, RDMA, QAT, by leveraging I/O virtualization technologies (IOMMU, interrupt remapping).

Acceleration

The Kata Containers runtime MUST support accelerated and user-space-based I/O operations for networking (e.g. DPDK) as well as storage through vhost-user sockets.

Scalability

The Kata Containers runtime MUST support scalable I/O through the SRIOV technology.

Virtualization overhead reduction

A compelling aspect of containers is their minimal overhead compared to bare metal applications. A container runtime should keep the overhead to a minimum in order to provide the expected user experience. The Kata Containers runtime implementation SHOULD be optimized for:

  • Minimal workload boot and shutdown times
  • Minimal workload memory footprint
  • Maximal networking throughput
  • Minimal networking latency

Testing and debugging

Continuous Integration

Each Kata Containers runtime pull request MUST pass at least the following set of container-related tests:

  • Unit tests: runtime unit tests coverage >75%
  • Functional tests: the entire runtime CLI and APIs
  • Integration tests: Docker and Kubernetes

Debugging

The Kata Containers runtime implementation MUST use structured logging in order to namespace log messages to facilitate debugging.