ip-masq-agent-v2

Based on the original ip-masq-agent, v2 aims to solve more specific networking cases, allow for more configuration options, and improve observability. This includes:

• Merging configuration from multiple sources
• Detecting conflicting configurations
• Fixing security vulnerabilities
• Quickly crashing on errors

Overview

The ip-masq-agent configures iptables rules to MASQUERADE traffic outside link-local (optional, enabled by default) and additional arbitrary IP ranges.

It creates an iptables chain called IP-MASQ-AGENT, which contains match rules for link local (169.254.0.0/16) and each of the user-specified IP ranges. It also creates a rule in POSTROUTING that jumps to this chain for any traffic not bound for a LOCAL destination.

IPs that match the rules (except for the final rule) in IP-MASQ-AGENT are not subject to MASQUERADE via the IP-MASQ-AGENT chain (they RETURN early from the chain). The final rule in the IP-MASQ-AGENT chain will MASQUERADE any non-LOCAL traffic.

RETURN in IP-MASQ-AGENT resumes rule processing at the next rule the calling chain, POSTROUTING. Take care to avoid creating additional rules in POSTROUTING that cause packets bound for your configured ranges to undergo MASQUERADE.

Launching the agent as a DaemonSet

This repo includes an example yaml file that can be used to launch the ip-masq-agent as a DaemonSet in a Kubernetes cluster.

kubectl create -f examples/ip-masq-agent.yaml

Configuring the agent

Important: You should not attempt to run this agent in a cluster where the Kubelet is also configuring a non-masquerade CIDR. You can pass --non-masquerade-cidr=0.0.0.0/0 to the Kubelet to nullify its rule, which will prevent the Kubelet from interfering with this agent.

By default, the agent is configured to treat the three private IP ranges specified by RFC 1918 as non-masquerade CIDRs. These ranges are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. To change this behavior, see the flags section below. The agent will also treat link-local (169.254.0.0/16) as a non-masquerade CIDR by default.

By default, the agent is configured to reload its configuration from the /etc/config/ directory in its container every 60 seconds.

The agent configuration file should be written in yaml or json syntax, and may contain three optional keys:

• nonMasqueradeCIDRs []string: A list strings in CIDR notation that specify the non-masquerade ranges.
• masqLinkLocal bool: Whether to masquerade traffic to 169.254.0.0/16. False by default.
• masqLinkLocalIPv6 bool: Whether to masquerade traffic to fe80::/10. False by default.

The agent will look for config files in its container at /etc/config/. This file can be provided via a ConfigMap, plumbed into the container by specifying it as a projected volume, and mounting it.

As a result, the agent can be reconfigured in a live cluster by creating or editing these ConfigMaps. Please ensure that your file name in the ConfigMaps matches the config file prefix: ip-masq-*.

This repo includes an example use-case. You can modify it to your needs and apply it to your cluster:

kubectl create configmap examples/config-custom.yaml

Note that we created the ConfigMap in the same namespace as the DaemonSet Pods, and named the ConfigMap to match the spec in examples/ip-masq-agent.yaml. This is necessary for the ConfigMap to appear in the Pods' filesystems.

Tolerance of multiple ConfigMaps allows custom keys to be defined while avoiding conflicts of any ConfigMaps that will need to be reconciled dynamically. This repo also provides an example of what might be configured by a cloud provider:

kubectl create configmap examples/config-reconciled.yaml

The cloud provider may wish to reconcile a ConfigMap so that it can be in-sync with the subnet of the cluster.

Agent Flags

The agent accepts multiple flags, which may be specified in the yaml file.

masq-chain

The name of the iptables chain to use. Default set to IP-MASQ-AGENT.

nomasq-all-reserved-ranges

Whether or not to masquerade all RFC reserved ranges when the configmap is empty. The default is false. When false, the agent will masquerade to every destination except the ranges reserved by RFC 1918 (namely 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16). When true, the agent will masquerade to every destination that is not marked reserved by an RFC. The full list of ranges is (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, 100.64.0.0/10, 192.0.0.0/24, 192.0.2.0/24, 192.88.99.0/24, 198.18.0.0/15, 198.51.100.0/24, 203.0.113.0/24, and 240.0.0.0/4). Note however, that this list of ranges is overridden by specifying the nonMasqueradeCIDRs key in the agent configmap.

enable-ipv6

Whether to configure ip6tables rules. Default is false.

resync-interval

How often to refresh the config (in seconds). Default set to 60.

klog also offers a range of flags that the agent inherits from (e.g. --v for log verbosity level).

Rationale

(from the incubator proposal)

This agent solves the problem of configuring the CIDR ranges for non-masquerade in a cluster (via iptables rules). Today, this is accomplished by passing a --non-masquerade-cidr flag to the Kubelet, which only allows one CIDR to be configured as non-masquerade. RFC 1918, however, defines three ranges (10/8, 172.16/12, 192.168/16) for the private IP address space.

Some users will want to communicate between these ranges without masquerade - for instance, if an organization's existing network uses the 10/8 range, they may wish to run their cluster and Pods in 192.168/16 to avoid IP conflicts. They will also want these Pods to be able to communicate efficiently (no masquerade) with each-other and with their existing network resources in 10/8. This requires that every node in their cluster skips masquerade for both ranges.

We are trying to eliminate networking code from the Kubelet, so rather than extend the Kubelet to accept multiple CIDRs, ip-masq-agent allows you to run a DaemonSet that configures a list of CIDRs as non-masquerade.

Contributing

This project welcomes contributions and suggestions.

Developing

Clone the repo to $GOPATH/src/github.com/Azure/ip-masq-agent-v2.

The build tooling is based on thockin/go-build-template.

Run make or make build to compile the ip-masq-agent. This will use a Docker image to build the agent, with the current directory volume-mounted into place. This will store incremental state for the fastest possible build. Run make all-build to build for all architectures.

Run make test to run the unit tests.

Run make container to build the container image. It will calculate the image tag based on the most recent git tag, and whether the repo is "dirty" since that tag (see make version). Run make all-container to build containers for all architectures.

Run make push to push the container image to REGISTRY. Run make all-push to push the container images for all architectures.

Run make clean to clean up.

Contribution requirements

Most contributions require you to agree to a Contributor License Agreement (CLA) declaring that you have the right to, and actually do, grant us the rights to use your contribution. For details, visit https://cla.opensource.microsoft.com.

When you submit a pull request, a CLA bot will automatically determine whether you need to provide a CLA and decorate the PR appropriately (e.g., status check, comment). Simply follow the instructions provided by the bot. You will only need to do this once across all repos using our CLA.

Code of Conduct

This project has adopted the Microsoft Open Source Code of Conduct. For more information see the Code of Conduct FAQ or contact opencode@microsoft.com with any additional questions or comments.

Trademarks

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