ip-masq-agent
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 ip-masq-agent.yaml
The spec in ip-masq-agent.yaml
specifies the kube-system
namespace for the DaemonSet Pods.
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/ip-masq-agent
file 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 to169.254.0.0/16
. False by default.masqLinkLocalIPv6 bool
: Whether to masquerade traffic tofe80::/10
. False by default.resyncInterval string
: The interval at which the agent attempts to reload config from disk. The syntax is any format accepted by Go's time.ParseDuration function.
The agent will look for a config file in its container at /etc/config/ip-masq-agent
. This file can be provided via a ConfigMap
, plumbed into the container via a ConfigMapVolumeSource
. As a result, the agent can be reconfigured in a live cluster by creating or editing this ConfigMap
.
This repo includes a directory-representation of a ConfigMap
that can configure the agent (the agent-config
directory). To use this directory to create the ConfigMap
in your cluster:
kubectl create configmap ip-masq-agent --from-file=agent-config --namespace=kube-system
Note that we created the ConfigMap
in the same namespace as the DaemonSet Pods, and named the ConfigMap
to match the spec in ip-masq-agent.yaml
. This is necessary for the ConfigMap
to appear in the Pods' filesystems.
Agent Flags
The agent accepts two flags, which may be specified in the yaml file.
masq-chain
: The name of the iptables
chain to use. By 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 configurate ip6tables rules. By default enable-ipv6
is false.
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 Pod
s in 192.168/16
to avoid IP conflicts. They will also want these Pod
s 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.
Incubator
This is a Kubernetes Incubator project. The incubator team for the project is:
- Current Owners: Rohit Ramkumar (@rramkumar1), Jing Ai (@jingax10)
- Original Author: Mike Taufen (@mtaufen)
- Sponsor: Tim Hockin (@thockin)
- Champion: Bowei Du (@bowei)
- SIG: sig-network Note: ip-masq-agent is subproject of sig-network,Incubator link not required.
Releasing
See RELEASE.
Developing
Clone the repo to $GOPATH/src/k8s.io/ip-masq-agent
.
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.