Introduction to Cilium & Hubble

What is Cilium?

Cilium is open source software for transparently securing the network connectivity between application services deployed using Linux container management platforms like Docker and Kubernetes.

At the foundation of Cilium is a new Linux kernel technology called eBPF, which enables the dynamic insertion of powerful security visibility and control logic within Linux itself. Because eBPF runs inside the Linux kernel, Cilium security policies can be applied and updated without any changes to the application code or container configuration.


If you’d like a video introduction to Cilium, check out this explanation by Thomas Graf, Co-founder of Cilium.

What is Hubble?

Hubble is a fully distributed networking and security observability platform. It is built on top of Cilium and eBPF to enable deep visibility into the communication and behavior of services as well as the networking infrastructure in a completely transparent manner.

By building on top of Cilium, Hubble can leverage eBPF for visibility. By relying on eBPF, all visibility is programmable and allows for a dynamic approach that minimizes overhead while providing deep and detailed visibility as required by users. Hubble has been created and specifically designed to make best use of these new eBPF powers.

Hubble can answer questions such as:

Service dependencies & communication map

  • What services are communicating with each other? How frequently? What does the service dependency graph look like?

  • What HTTP calls are being made? What Kafka topics does a service consume from or produce to?

Network monitoring & alerting

  • Is any network communication failing? Why is communication failing? Is it DNS? Is it an application or network problem? Is the communication broken on layer 4 (TCP) or layer 7 (HTTP)?

  • Which services have experienced a DNS resolution problem in the last 5 minutes? Which services have experienced an interrupted TCP connection recently or have seen connections timing out? What is the rate of unanswered TCP SYN requests?

Application monitoring

  • What is the rate of 5xx or 4xx HTTP response codes for a particular service or across all clusters?

  • What is the 95th and 99th percentile latency between HTTP requests and responses in my cluster? Which services are performing the worst? What is the latency between two services?

Security observability

  • Which services had connections blocked due to network policy? What services have been accessed from outside the cluster? Which services have resolved a particular DNS name?


If you’d like a video introduction to Hubble, check out eCHO episode 2: Introduction to Hubble.

Why Cilium & Hubble?

eBPF is enabling visibility into and control over systems and applications at a granularity and efficiency that was not possible before. It does so in a completely transparent way, without requiring the application to change in any way. eBPF is equally well-equipped to handle modern containerized workloads as well as more traditional workloads such as virtual machines and standard Linux processes.

The development of modern datacenter applications has shifted to a service-oriented architecture often referred to as microservices, wherein a large application is split into small independent services that communicate with each other via APIs using lightweight protocols like HTTP. Microservices applications tend to be highly dynamic, with individual containers getting started or destroyed as the application scales out / in to adapt to load changes and during rolling updates that are deployed as part of continuous delivery.

This shift toward highly dynamic microservices presents both a challenge and an opportunity in terms of securing connectivity between microservices. Traditional Linux network security approaches (e.g., iptables) filter on IP address and TCP/UDP ports, but IP addresses frequently churn in dynamic microservices environments. The highly volatile life cycle of containers causes these approaches to struggle to scale side by side with the application as load balancing tables and access control lists carrying hundreds of thousands of rules that need to be updated with a continuously growing frequency. Protocol ports (e.g. TCP port 80 for HTTP traffic) can no longer be used to differentiate between application traffic for security purposes as the port is utilized for a wide range of messages across services.

An additional challenge is the ability to provide accurate visibility as traditional systems are using IP addresses as primary identification vehicle which may have a drastically reduced lifetime of just a few seconds in microservices architectures.

By leveraging Linux eBPF, Cilium retains the ability to transparently insert security visibility + enforcement, but does so in a way that is based on service / pod / container identity (in contrast to IP address identification in traditional systems) and can filter on application-layer (e.g. HTTP). As a result, Cilium not only makes it simple to apply security policies in a highly dynamic environment by decoupling security from addressing, but can also provide stronger security isolation by operating at the HTTP-layer in addition to providing traditional Layer 3 and Layer 4 segmentation.

The use of eBPF enables Cilium to achieve all of this in a way that is highly scalable even for large-scale environments.

Functionality Overview

Protect and secure APIs transparently

Ability to secure modern application protocols such as REST/HTTP, gRPC and Kafka. Traditional firewalls operates at Layer 3 and 4. A protocol running on a particular port is either completely trusted or blocked entirely. Cilium provides the ability to filter on individual application protocol requests such as:

  • Allow all HTTP requests with method GET and path /public/.*. Deny all other requests.

  • Allow service1 to produce on Kafka topic topic1 and service2 to consume on topic1. Reject all other Kafka messages.

  • Require the HTTP header X-Token: [0-9]+ to be present in all REST calls.

See the section Layer 7 Policy in our documentation for the latest list of supported protocols and examples on how to use it.

Secure service to service communication based on identities

Modern distributed applications rely on technologies such as application containers to facilitate agility in deployment and scale out on demand. This results in a large number of application containers to be started in a short period of time. Typical container firewalls secure workloads by filtering on source IP addresses and destination ports. This concept requires the firewalls on all servers to be manipulated whenever a container is started anywhere in the cluster.

In order to avoid this situation which limits scale, Cilium assigns a security identity to groups of application containers which share identical security policies. The identity is then associated with all network packets emitted by the application containers, allowing to validate the identity at the receiving node. Security identity management is performed using a key-value store.

Secure access to and from external services

Label based security is the tool of choice for cluster internal access control. In order to secure access to and from external services, traditional CIDR based security policies for both ingress and egress are supported. This allows to limit access to and from application containers to particular IP ranges.

Simple Networking

A simple flat Layer 3 network with the ability to span multiple clusters connects all application containers. IP allocation is kept simple by using host scope allocators. This means that each host can allocate IPs without any coordination between hosts.

The following multi node networking models are supported:

  • Overlay: Encapsulation-based virtual network spanning all hosts. Currently VXLAN and Geneve are baked in but all encapsulation formats supported by Linux can be enabled.

    When to use this mode: This mode has minimal infrastructure and integration requirements. It works on almost any network infrastructure as the only requirement is IP connectivity between hosts which is typically already given.

  • Native Routing: Use of the regular routing table of the Linux host. The network is required to be capable to route the IP addresses of the application containers.

    When to use this mode: This mode is for advanced users and requires some awareness of the underlying networking infrastructure. This mode works well with:

    • Native IPv6 networks

    • In conjunction with cloud network routers

    • If you are already running routing daemons

Load Balancing

Cilium implements distributed load balancing for traffic between application containers and to external services and is able to fully replace components such as kube-proxy. The load balancing is implemented in eBPF using efficient hashtables allowing for almost unlimited scale.

For north-south type load balancing, Cilium’s eBPF implementation is optimized for maximum performance, can be attached to XDP (eXpress Data Path), and supports direct server return (DSR) as well as Maglev consistent hashing if the load balancing operation is not performed on the source host.

For east-west type load balancing, Cilium performs efficient service-to-backend translation right in the Linux kernel’s socket layer (e.g. at TCP connect time) such that per-packet NAT operations overhead can be avoided in lower layers.

Bandwidth Management

Cilium implements bandwidth management through efficient EDT-based (Earliest Departure Time) rate-limiting with eBPF for container traffic that is egressing a node. This allows to significantly reduce transmission tail latencies for applications and to avoid locking under multi-queue NICs compared to traditional approaches such as HTB (Hierarchy Token Bucket) or TBF (Token Bucket Filter) as used in the bandwidth CNI plugin, for example.

Monitoring and Troubleshooting

The ability to gain visibility and to troubleshoot issues is fundamental to the operation of any distributed system. While we learned to love tools like tcpdump and ping and while they will always find a special place in our hearts, we strive to provide better tooling for troubleshooting. This includes tooling to provide:

  • Event monitoring with metadata: When a packet is dropped, the tool doesn’t just report the source and destination IP of the packet, the tool provides the full label information of both the sender and receiver among a lot of other information.

  • Metrics export via Prometheus: Key metrics are exported via Prometheus for integration with your existing dashboards.

  • Hubble: An observability platform specifically written for Cilium. It provides service dependency maps, operational monitoring and alerting, and application and security visibility based on flow logs.