amazon-vpc-cni-k8s

Networking plugin for pod networking in Kubernetes using Elastic Network Interfaces on AWS.

Setup

Download the latest version of the yaml and apply it the cluster.

kubectl apply -f aws-k8s-cni.yaml

Launch kubelet with network plugins set to cni (--network-plugin=cni), the cni directories configured (--cni-config-dir and --cni-bin-dir) and node ip set to the primary IPv4 address of the primary ENI for the instance (--node-ip=$(curl http://169.254.169.254/latest/meta-data/local-ipv4)). It is also recommended to set --max-pods equal to (the number of ENIs for the instance type * (the number of IPs per ENI - 1)) + 2 see to prevent scheduling that exceeds the IP resources available to the kubelet.

The default manifest expects --cni-conf-dir=/etc/cni/net.d and --cni-bin-dir=/opt/cni/bin.

L-IPAM requires following IAM policy:

 {
     "Effect": "Allow",
     "Action": [
         "ec2:CreateNetworkInterface",
         "ec2:AttachNetworkInterface",
         "ec2:DeleteNetworkInterface",
         "ec2:DetachNetworkInterface",
         "ec2:DescribeNetworkInterfaces",
         "ec2:DescribeInstances",
         "ec2:ModifyNetworkInterfaceAttribute",
         "ec2:AssignPrivateIpAddresses"
     ],
     "Resource": [
         "*"
     ]
 },
 {
     "Effect": "Allow",
     "Action": "ec2:CreateTags",
     "Resource": "arn:aws:ec2:*:*:network-interface/*"
 },

Building

• make defaults to make build-linux that builds the Linux binaries.
• make docker-build uses a docker container (golang:1.10) to build the binaries.
• make docker will create a docker container using the docker-build with the finished binaries, with a tag of amazon/amazon-k8s-cni:latest
• unit-test, lint and vet provide ways to run the respective tests/tools and should be run before submitting a PR.

Components

There are 2 components:

• CNI Plugin, which will wire up host's and pod's network stack when called.
• L-IPAMD, which is a long running node-Local IP Address Management (IPAM) daemon, is responsible for:
  • maintaining a warm-pool of available IP addresses, and
  • assigning an IP address to a Pod.

The details can be found in Proposal: CNI plugin for Kubernetes networking over AWS VPC.

Troubleshooting Guide provides tips on how to debug and troubleshoot CNI.

ENI Allocation

When a worker node first joins the cluster, there is only 1 ENI along with all of its addresses in the ENI. Without any configuration, ipamD always try to keep one extra ENI.

When number of pods running on the node exceeds the number of addresses on a single ENI, the CNI backend start allocating a new ENI and start using following allocation scheme:

For example, a m4.4xlarge node can have up to 8 ENIs, and each ENI can have up to 30 IP addresses. ( https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-eni.html ).

• If the number of current running Pods is between 0 to 29, ipamD will allocate one more eni. And Warm-Pool size is 2 eni * (30 -1) = 58
• If the number of current running Pods is between 30 and 58, ipamD will allocate 2 more eni. And Warm-Pool size is 3 eni * (30 -1) = 87

CNI Configuration Variables

The Amazon VPC CNI plugin for Kubernetes supports a number of configuration options, which are set through environment variables. The following environment variables are available, and all of them are optional.

AWS_VPC_CNI_NODE_PORT_SUPPORT
Type: Boolean
Default: true
Specifies whether NodePort services are enabled on a worker node's primary network interface. This requires additional iptables rules and that the kernel's reverse path filter on the primary interface is set to loose.

AWS_VPC_K8S_CNI_CUSTOM_NETWORK_CFG
Type: Boolean
Default: false
Specifies that your pods may use subnets and security groups that are independent of your worker node's VPC configuration. By default, pods share the same subnet and security groups as the worker node's primary interface. Setting this variable to true causes ipamD to use the security groups and VPC subnet in a worker node's ENIConfig for elastic network interface allocation. You must create an ENIConfig custom resource definition for each subnet that your pods will reside in, and then annotate each worker node to use a specific ENIConfig (multiple worker nodes can be annotated with the same ENIConfig). Worker nodes can only be annotated with a single ENIConfig at a time, and the subnet in the ENIConfig must belong to the same Availability Zone that the worker node resides in. For more information, see aws#165.

AWS_VPC_K8S_CNI_EXTERNALSNAT
Type: Boolean
Default: false
Specifies whether an external NAT gateway should be used to provide SNAT of secondary ENI IP addresses. If set to true, the SNAT iptables rule and off-VPC IP rule are not applied, and these rules are removed if they have already been applied.
Disable SNAT if you need to allow inbound communication to your pods from external VPNs, direct connections, and external VPCs, and your pods do not need to access the Internet directly via an Internet Gateway. However, your nodes must be running in a private subnet and connected to the internet through an AWS NAT Gateway or another external NAT device.

WARM_ENI_TARGET
Type: Integer
Default: 1
Specifies the number of free elastic network interfaces (and all of their available IP addresses) that the ipamD daemon should attempt to keep available for pod assignment on the node. By default, ipamD attempts to keep 1 elastic network interface and all of its IP addresses available for pod assignment.
The number of IP addresses per network interface varies by instance type. For more information, see IP Addresses Per Network Interface Per Instance Type in the Amazon EC2 User Guide for Linux Instances. For example, an m4.4xlarge launches with 1 network interface and 30 IP addresses. If 5 pods are placed on the node and 5 free IP addresses are removed from the IP address warm pool, then ipamD attempts to allocate more interfaces until WARM_ENI_TARGET free interfaces are available on the node.
If WARM_IP_TARGET is set, then this environment variable is ignored and the WARM_IP_TARGET behavior is used instead.

WARM_IP_TARGET
Type: Integer
Default: None
Specifies the number of free IP addresses that the ipamD daemon should attempt to keep available for pod assignment on the node. For example, if WARM_IP_TARGET is set to 10, then ipamD attempts to keep 10 free IP addresses available at all times. If the elastic network interfaces on the node are unable to provide these free addresses, ipamD attempts to allocate more interfaces until WARM_IP_TARGET free IP addresses are available.
This environment variable overrides WARM_ENI_TARGET behavior.

Notes

L-IPAMD(aws-node daemonSet) running on every worker node requires access to kubernetes API server. If it can not reach kubernetes API server, ipamD will exit and CNI will not be able to get any IP address for Pods. Here is a way to confirm if L-IPAMD has access to the kubernetes API server.

# find out kubernetes service IP, e.g. 10.0.0.1
kubectl get svc kubernetes
NAME         TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)   AGE
kubernetes   ClusterIP   10.0.0.1   <none>        443/TCP   29d

# ssh into worker node, check if worker node can reach API server
telnet 10.0.0.1 443
Trying 10.0.0.1...
Connected to 10.0.0.1.
Escape character is '^]'.  <-------- kubernetes API server is reachable

Contributing

See CONTRIBUTING.md