MetalLB is a load-balancer implementation for bare metal Kubernetes clusters, using BGP.
Kubernetes does not offer an implementation of network load-balancers (Service
spec.type=LoadBalancer) for bare metal clusters. The
implementations of Network LB that Kubernetes does ship with are all glue code
that calls out to various IaaS platforms (GCP, AWS, Azure…). If you’re not
running on one of those platforms,
LoadBalancers will remain in the “pending”
state indefinitely when created.
Bare metal cluster operators are left with two lesser tools to bring user
traffic into their clusters,
externalIPs services. Both of
these options have significant downsides for production use, which makes bare
metal clusters second class citizens in the Kubernetes ecosystem.
MetalLB aims to redress this imbalance by offering a Network LB implementation that integrates with standard network equipment, so that external services on bare metal clusters also “just work” as much as possible.
MetalLB requires the following to function:
- A Kubernetes cluster, running Kubernetes 1.8.0 or later, that does not already have network load-balancing functionality.
- One or more BGP capable routers that support 4-byte AS numbers (RFC 6793).
- Some IPv4 addresses for MetalLB to hand out.
The requirements page goes into more detail.
You should also note that MetalLB is currently a young project, so you should treat it as an “alpha” product. The project maturity page explains what that implies.
Want to test-drive MetalLB? Follow the tutorial to set up a self-contained MetalLB in minikube.
You might also find the design document useful to better understand how MetalLB operates.
We welcome contributions in all forms. Please check out the contributing guide for more information.
One lightweight way you can contribute is to tell us that you’re using MetalLB, which will give us warm fuzzy feelings :).