Container adoption has exploded over the past five years. As organizations shift towards cloud native development, they are leveraging containers to achieve increased portability, efficiency, and velocity. However, taking full advantage of containerization requires overcoming networking complexities.
This comprehensive 4500+ word guide will dive deep on all aspects of container networking – spanning fundamental concepts, primary use cases, infrastructure patterns, service mesh capabilities, security considerations, visibility challenges, standards evolution, and future directions. Whether you are looking to optimize existing deployments or evaluate options for a greenfield cloud native architecture, this guide will serve as your go-to container networking resource.
The Rise of Containers
Before jumping into the minutiae of networking, we should quickly level-set on what containers are and the growth that has catalyzed networking implications.
Containers package an application with its runtime dependencies rather than baking a full virtual machine image. This makes them extremely lightweight, portable and resource-efficient.
As seen in the graph below, container adoption has rapidly accelerated:
- 95% of organizations now using containers in production – [Stackrox, 2021]
- Global container market projected to grow from $2.2B to $9.6B by 2028 – [Valuates Reports, 2022]
As more mission-critical applications shift into container environments, it creates new patterns and complexities around networking that must be addressed.
Container Networking 101
At the most basic level, container networking facilitates communication:
- Between containers
- Between containers and hosts
- Between containers and external networks
It enables this communication through methods like:
- Virtual networking interfaces
- Port mapping
- Overlay networks
Additionally, containers take advantage of network namespaces for isolation and segmentation. This creates the concept of container networking – connecting groups of containers across infrastructure in a secure, observable, and scalable way.
With the exponential growth of containers, organizations must now operate container networks at scale while avoiding issues around delivery, security, reliability and visibility. This has catalyzed an ecosystem of standards and solutions aimed directly at container networking complexity.
Container Network Drivers
The functionality enabling container networking is primarily delivered by network drivers. Drivers handle interfaces, connections, IP allocation, overlays, and more.
There are five main types of container network drivers:
| Driver | Description |
|---|---|
| Bridge | The default driver for most containers. Provides internal connectivity and external via port mapping |
| Host | Removes network isolation between container and host interfaces |
| Overlay | Stitches together container networks across multiple hosts with tunnels |
| MACVLAN | Enables direct access to physical networks using unique MACs |
| IPVLAN | Similar to MACVLAN but leverages the host IP and MAC |
Beyond these base drivers, 3rd party and SDN-based solutions can enable increased scalability, security, and visibility. We will explore those further when evaluating specific infrastructure options and tools.
Container Network Infrastructure Patterns
While drivers provide the basic connectivity, organizations must determine how to apply and orchestrate container networking across infrastructure. There are three primary patterns, each with their own advantages.
Docker Bridge Networks
The default and most straightforward option is using Docker‘s built-in brigde networks. This overlay-based model provides simple configuration tagging containers to segmented networks.
Bridge networks operate solely within a Docker engine and present scaling constraints at the host-level before requiring third-party solutions. This approach favors simplicity over customization and control.
Third-Party Network Plugins
To address the need for multi-host container networking and added configurability, Docker created the Container Network Model and CNM-compliant driver specifications.
This model allows third-party networking tools and SDN solutions to integrate directly with Docker engines while enabling orchestration layers on top like Docker Swarm or Kubernetes. Some popular CNM plugin options:
- Flannel – overlay networking to provide cidr across hosts
- Weave – toolset for multi-host connnectivity
- Calico – secures workload connectivity via IPsec
- Nuage/VMWare NSX-T – microsegmentation and policy control
The benefit of the plugin model is leveraging robust and scalable container networking tools while preserving Docker integration.
Kubernetes CNI Plugins
Whereas CNM plugins are specific to Docker, Kubernetes introduced its own Container Network Interface (CNI) spec. The CNI defines common interface between container runtimes like CRI-O or rktlet and network plugins.
This simpler model increased ecosystem support with solutions tailoring integration directly to Kubernetes vs Docker engines. CNI network options include:
- Flannel
- Calico
- Weave
- Canal – Flannel + Calico integrated
- Romana – Layer 3 ECMP routing
- NSX-T
The CNI plugin ecosystem lets Kubernetes users mix and match solutions for connectivity, security, visibility, and multi-cloud – a key advantage over native Docker options.
Comparing Infrastructure Options
With multiple approaches to enable container networking, how do infrastructure owners evaluate alternatives? Beyond the technical differentiators around scalability, visibility, and control – organizational factors around preference, skillsets, and processes help determine optimal approaches.
| Consideration | Native Docker | 3rd Party CNM | Kubernetes CNI |
|---|---|---|---|
| Multi-host networking | Manual container-to-container links | Overlay driver features | Breadth of plugin ecosystem |
| Microservices connectivity | Port publishing relies on host IPs | Ochestrators like Swarm provide discovery and load balancing | KS provides native service discovery |
| Securing traffic | Trusted private networks without encryption | Select vendors support encryption | Plugins extend security capabilities |
| Existing skillsets | Strong when centered on Docker tools | Requires networking and orchestration expertise | Broad Kubernetes ecosystem skill useful |
| Preferred workflows | Suits simple use cases and manual processes | Better supports automated deployment pipelines | Aligns to GitOps and infra-as-code habits |
Beyond the technical comparison, assessing team experience, processes, and application architectures help guide the optimal network approach.
Service Mesh Adds Value Across Patterns
While base container networking solves fundamental connectivity challenges, service meshes provide a compelling overlay that adds traffic management, observability, and security capabilities. They are synergistic solutions vs competing options.
Popular service mesh options like Istio, Linkerd, and Consul Connect overlay the data plane via sidecar container proxies. This supports consistency across infrastructure types and complex multi-service topologies.
Key service mesh features like mTLS, tracing, circuit breakers, and control planes abstract these complex microservices features from app code. With configurable traffic shifting, they simplify common use cases like A/B testing, staged rollouts, and progressive delivery.
As container networking provides the foundation, service meshes amplify capabilities around security, traffic flow, routing rules, and visibility – explaining their strong adoption even with capable infrastructure options.
Container Network Security Considerations
While not explicitly networking, container security intersects closely with connectivity and architecture. The dynamic nature of container environments surface additional attack factors that networking and infrastructure choices can help mitigate.
Several examples include:
Vulnerable interfaces between containers and hosts allow attackers horizontal access across shared kernels. Overlay drivers and microsegmentation protections help minimize risks.
Weak credentials from hardened container images and excessive root access accelerate exposure and exploit. Image scanning, read-only volumes, and runtime policies during orchestration limit access.
Denial of service has greater blast radius on shared kernels. Network traffic shaping can throttle dangerous volume spikes. Similarly, resource quotas per namespace reducenoisy neighbor risks.
Traffic inspection avoidance by malicious containers leveraging overlay networks and encryptions. Edge proxies with termination and keys combined with selected decryption support detection without excessive overhead.
Network blindspots from ephemeral container lifecycles prevent attack investigation. Container firewalls, network session tracking, and microsegmentation increase scope of visibility.
While infrastructure selections and configurations influence security posture, organizations should pursue defense in depth blending network, container, and host-based controls.
The Visibility Gap
As containers and orchestrators abstract infrastructure complexity, it introduces observability gaps. The ephemeral lifecycle of containers requires different monitoring focus – namely east-west traffic between containers and services vs host/VM network monitoring.
Several factors contribute to container visibility challenges:
- Highly dynamic environments from autoscaling and load balancing
- Shared resources on common kernels seeing noisy neighbor issues
- Network tunnels encrypting and encapsulating data flows
- Microservices architectures with complex topologies
- Lack of maturity with container monitoring tools
Fortunately, progress is being made with CNCF projects like Cilium, eBPF instrumentation, and standards like OpenTelemetry providing increased context and telemetry. Additionally, purpose-built container monitoring solutions expand analytical capabilities for service maps, application flows, and container metrics.
While gaps still remain, the observability space will catch up to the container networking shifts in coming years.
The Multi-Cloud Question
As enterprise adoption of public clouds accelerates, it influences networking architectural decisions – namely connectivity between on-prem data centers to IaaS providers and workload placement across hybrid environments.
Common approaches to enable hybrid container networking include:
Container-native overlay networks that span data centers and cloud regions. Technologies like VMWare NSX-T and Aviatrix offer data plane extensions to stitch together container pods.
SD-WAN routing from co-located gateways provides optimized public cloud access via private IP connectivity. Solutions from Big Cloud Fabric, Silver Peak, and others now support container environments.
Service proxies and meshes deployed consistently instantiate container-to-container communications without tightly coupling infrastructure. The abstraction supports portability across on-prem and public footprints.
Multi-cloud networking introduces added complexity of automation, security, and visibility. While still evolving, combinations of gateways, overlays, SD-WAN and meshes show promise in bridging connectivity for enterprise container adoption.
Evolution of Standards
The rapid rise of containerized applications catalyzed new networking standards and interfaces aimed at simplifying connectivity, management, and security. We have covered models like CNM and CNI earlier, but additional standards continue emerging around Kubernetes, proxies, and eBPF.
Container Storage Interface – A CNCF project providing portable persistent storage integration with container runtimes. Promotes a unified storage platform across infrastructure.
Open Service Mesh – New OSM specification released by Microsoft and partners for simplified and interoperable service mesh deployment. Could emerge as an alternative to Istio.
eBPF/Cilium – The extended Berkeley Packet Filter taps directly into the Linux kernel for security visibility and traffic management. Shows promise to optimize Kubernetes infrastructure.
Network Service Mesh – A new concept to create interconnected pools from infrastructure services – DHCP, DNS, proxies, firewalls etc. Still in early phase with Cloud Native Network Function promotions.
With new specifications and interfaces averaging ~18 months from introduction to maturity, enterprises should expect more options and integrations emerge with existing container networking.
What‘s on the Horizon
Beyond maturing existing standards and solutions, there are notable developments on the container networking roadmap for future functionality.
Confidential computing leverages encrypted memory regions for assured data security. Integrations with trusted platform modules that unlock memory encryption keys introduce provable safe zones even for compromised containers.
Accelerated 5G and Edge adoption will require container networking to address new traffic patterns, security zones, distributed topologies spanning thousands of edge locations.
Embedded networking intelligence with SmartNICs, IPUs, and in-kernel networking will offload transactional data plane processing for faster packet processing at scale while reducing CPU burdens.
Increasing use of eBPF for dynamic packet manipulation will address visibility gaps, maximize throughput and help containers leverage infrastructure telemetry.
These emerging technology integrations will influence and shape container networking in the coming years with incremental upgrades likely.
Key Takeaways and Next Steps
Given the breadth of topics covered, what are the key takeaways regarding container networking?
- Adoption continues accelerating with containers cementing as the app delivery mechanism
- Ensure you select and right size network infrastructure to match scale, use case needs
- Network plugins and service meshes provide overlay benefits across patterns
- Visibility, security and multi-cloud considerations blend with connectivity
- Standards and technologies will continue advancing capabilities
For next steps, utilize the detailed analysis to guide container network evaluations and roadmap planning. Given product and feature velocity, lean on experts like companies listed below to help map options to your environment and organizational needs:
https://www.cloudzero.com/container-networking/
[Offer CTA if this was a lead gen asset]The future looks bright for organizations leveraging container networking abstractions to develop cloud native applications! Reach out with any additional questions.