Containerization in Cloud-Native Application Development
Containerization is a crucial aspect of cloud-native application development, with Kubernetes standing out as a leading container orchestration platform. This article explores the concept of containerization, its defining features, the role of Kubernetes within this framework, its organizational structure, and its approach to managing persistent storage and data protection. Additionally, we will examine the Container Storage Interface (CSI) that connects Kubernetes to storage hardware and highlight key Kubernetes management solutions provided by major storage vendors.
Understanding Containerization
Containerization can be viewed as a type of virtualization, best explained through a comparison with traditional server virtualization technology. In server virtualization environments—such as VMware or Nutanix—a hypervisor layer is created to abstract the physical resources of a server, enabling the deployment of numerous logical servers, known as virtual machines.
In contrast, application containerization bypasses the hypervisor and operates directly with the server’s operating system. Containers bundle all necessary elements for an application to function, allowing for rapid creation, scaling, and termination. Since containers are lighter than virtual machines—eliminating the need for the hypervisor—they consume fewer server resources and offer excellent portability across both on-premises and cloud environments, making them ideal for handling workloads that experience sudden spikes in demand, particularly in web applications.
Furthermore, containers embrace the microservices architecture, which breaks down application functionalities into small services built around application programming interfaces (APIs). This contrasts with traditional monolithic applications and aligns well with iterative development methodologies characteristic of DevOps.
What is Kubernetes?
Kubernetes is a prominent container orchestrator, although it is not the only option available. Other solutions like Apache Mesos, Docker Swarm, Nomad, and Red Hat OpenShift exist, along with cloud offerings such as AWS Elastic Container Service (ECS), Azure Kubernetes Service, and Google Kubernetes Engine. VMware also provides Tanzu products for managing Kubernetes in virtualized environments.
Container orchestrators like Kubernetes handle various functions, including the creation, management, automation, load balancing, and hardware integration of containers. In Kubernetes terms, these units are referred to as “pods,” which comprise one or more containers. Of all the container orchestrators, Kubernetes holds a dominant market position, capturing over 97% of the market share.
Organizational Structure of Kubernetes
The foundational element within Kubernetes is the container, which encapsulates the application’s runtime, code, dependencies, and libraries. Containers are stateless, meaning they do not retain any data or prior state information, which contributes to their portability and scalability. However, this stateless nature can also pose challenges.
Clusters are aggregates that contain pods, which host and manage these containers. Containers can serve different roles—such as user interface and backend database—yet they remain on the same node (physical server or virtual machine) to facilitate rapid communication.
Nodes are the physical or virtual machines executing the pods. They can be categorized as master nodes, which manage the deployment and status of the Kubernetes cluster, or worker nodes, which execute containers as assigned by the master nodes. The various master node components include the API server for cluster interactions, a scheduler for optimizing pod distribution, a controller manager for maintaining the desired state of the cluster, and etcd, a key-value store for cluster state information.
Worker nodes consist of Kubelets, which establish the link between the worker node and the control plane, kube-proxy for network communications, and container runtime for executing containers.
Challenges of Storage in Kubernetes
Kubernetes storage is fundamentally ephemeral, meaning it does not persist beyond the lifecycle of the container. Native Kubernetes storage is typically integrated into the container and relies on temporary scratch space that exists only while the Kubernetes pod is active. However, enterprise applications often depend on persistent storage, and Kubernetes does offer solutions to address this need.
Achieving Persistent Storage with Kubernetes
Kubernetes enables persistent storage functionality that supports various formats, including file, block, and object storage, as well as data services such as databases. While it is possible to reference storage from within the pod, it is not advisable due to portability concerns. Instead, Kubernetes employs Persistent Volumes (PVs) and Persistent Volume Claims (PVCs) to delineate storage requirements and application needs in a portable manner.
A PV is a defined storage volume within the cluster, characterized by performance and capacity metrics, and it includes details such as performance/cost class, capacity, volume plugins, and access credentials. Conversely, a PVC functions as a request for storage for the application within Kubernetes and is designed to be portable, allowing it to accompany the containerized application.
PVs are grouped into storage classes, which define the storage volume plugin, external providers, and CSI drivers used. One storage class may be designated as “default” to streamline storage requests.
What is the Container Storage Interface (CSI)?
The Container Storage Interface (CSI) provides a standardized approach for storage providers to expose their capabilities to container orchestration systems like Kubernetes. More than 130 CSI drivers are currently available for hardware and cloud file, block, and object storage formats. CSI offers a framework for configuring external persistent storage and enables advanced features such as snapshots and cloning.
A CSI volume can define PVs, allowing the creation of PVs and storage classes that interface with external storage defined by a CSI plugin, which is provisioned in response to a PVC.
Storage Vendor Solutions for Kubernetes Storage and Data Protection
Given the modular nature of Kubernetes, storage vendors have developed management layers to simplify storage provisioning and data service processes for administrators. Notable companies like Dell EMC, IBM, HPE, Hitachi, NetApp, and Pure Storage have created container management platforms that facilitate ease of integration for storage and data protection requirements in code while allowing traditional IT operations to be performed without extensive expertise.
These vendors leverage CSI drivers to manage storage provisioning and backup, accommodating various storage environments, including cloud systems.
Key Offerings from Storage Vendors
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Dell Container Storage Modules (CSM): Based on CSI drivers, Dell’s CSMs enhance automation and control, facilitating access to storage array features for customers. These modules support functionality such as replication, observability, resilience, application mobility, snapshots, access control, and encryption.
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IBM’s Red Hat OpenShift: Acquired in 2018, OpenShift enables management of Kubernetes persistent volume claims (PVCs) through CSI drivers, allowing seamless requests for storage resources supported by many PV plugins in various environments.
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HPE’s Ezmeral Runtime Enterprise: This platform provides capabilities for managing cloud-native applications using Kubernetes while streamlining data management and persistent storage across various infrastructures.
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Hitachi Kubernetes Service (HKS): HKS allows customers to manage container storage across on-premises and cloud environments, employing CSI drivers to manage persistent volumes directly on Kubernetes nodes.
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NetApp Astra: NetApp’s Astra solution encompasses components for managing the application lifecycle, data management in public clouds, and storage provisioning via CSI, ensuring smooth deployment and management of containerized workloads.
- Pure Storage Portworx: Portworx offers integrated provisioning, connectivity, and performance tuning for Kubernetes clusters, supporting diverse storage options and advanced functionalities like backup and disaster recovery.
In summary, containerization and Kubernetes are instrumental in modern application development, driving efficiency and scalability. Understanding their structures, capabilities, and the storage solutions available enhances effective deployment and management in today’s cloud-centric environments.