Netassert

NetAssert is a command line tool that enables you to check the network connectivity between Kubernetes objects such as Pods, Deployments, DaemonSets, and StatefulSets, as well as test their connectivity to remote hosts or IP addresses. NetAssert v2 is a rewrite of original NetAssert tool in Go that utilises the ephemeral container support in Kubernetes to verify network connectivity. NetAssert test(s) are defined in YAML format. NetAssert currently supports TCP and UDP protocols:

• To perform a TCP test, only a scanner container is used. This container requires no privileges nor any Linux capabilities.

• To run a UDP test, a sniffer ephemeral container is injected into the target Pod which requires cap_raw capabilities to read data from the network interface. During UDP testing, NetAssert runs both container scanner and sniffer container images which are injected as ephemeral containers into running Pods.

The sniffer and scanner container images can be downloaded from:

• docker.io/controlplane/netassertv2-l4-client:latest
  • Used for both TCP and UDP testing and acts as a Layer 4 (TCP/UDP) client
  • Requires no privileges nor any Linux capabilities.
• docker.io/controlplane/netassertv2-packet-sniffer:latest
  • Used for UDP testing only, injected at the destination to capture packet and search for specific string in the payload
  • requires cap_raw capabilities to read data from the network interface

NetAssert utilises the above containers during test and configures them using environment variables. The list of environment variables that are used can be found here and here. It is possible to override the sniffer and scanner images from command line during a run, so one can also bring their own container image(s) as long as they support the same environment variables.

Installation

Download the latest stable version of NetAssert from the releases page

Test specification

NetAssert v2 tests are written in YAML format. Each test is a YAML document which supports the following mappings:

• A YAML document is a list of NetAssert test. Each test has the following keys:
  • name: a scalar representing the name of the connection
  • type: a scalar representing the type of connection, only "k8s" is supported at this time
  • protocol: a scalar representing the protocol used for the connection, which must be "tcp" or "udp"
  • targetPort: an integer scalar representing the target port used by the connection
  • timeoutSeconds: an integer scalar representing the timeout for the connection in seconds
  • attempts: an integer scalar representing the number of connection attempts for the test
  • exitCode: an integer scalar representing the expected exit code from the ephemeral/debug container(s)
  • src: a mapping representing the source Kubernetes resource, which has the following keys:
    • k8sResource: a mapping representing a Kubernetes resource with the following keys:
      • kind: a scalar representing the kind of the Kubernetes resource, which can be deployment, statefulset, daemonset or pod
      • name: a scalar representing the name of the Kubernetes resource
      • namespace: a scalar representing the namespace of the Kubernetes resource
  • dst: a mapping representing the destination Kubernetes resource or host, which can have one of the the following keys i.e both k8sResource and host are not supported at the same time :
    • k8sResource: a mapping representing a Kubernetes resource with the following keys:
      • kind: a scalar representing the kind of the Kubernetes resource, which can be deployment, statefulset, daemonset or pod
      • name: a scalar representing the name of the Kubernetes resource
      • namespace: a scalar representing the namespace of the Kubernetes resource. (Note: Only allowed when protocol is "tcp")
    • host: a mapping representing a host/node with the following key:
      • name: a scalar representing the name or IP address of the host/node. (Note: Only allowed when protocol is "tcp" or "udp", but not both at the same time)

---
- name: busybox-deploy-to-echoserver-deploy
  type: k8s
  protocol: tcp
  targetPort: 8080
  timeoutSeconds: 67
  attempts: 3
  exitCode: 0
  src:
    k8sResource:
      kind: deployment
      name: busybox
      namespace: busybox
  dst:
    k8sResource:
      kind: deployment
      name: echoserver
      namespace: echoserver
#######
#######
- name: busybox-deploy-to-core-dns
  type: k8s
  protocol: udp
  targetPort: 53
  timeoutSeconds: 67
  attempts: 3
  exitCode: 0
  src:
    k8sResource:
      kind: deployment
      name: busybox
      namespace: busybox
  dst:
    k8sResource:
      kind: deployment
      name: coredns
      namespace: kube-system
######
######
- name: busybox-deploy-to-web-statefulset
  type: k8s
  protocol: tcp
  targetPort: 80
  timeoutSeconds: 67
  attempts: 3
  exitCode: 0
  src:
    k8sResource: # this is type endpoint
      kind: deployment
      name: busybox
      namespace: busybox
  dst:
    k8sResource: ## this is type endpoint
      kind: statefulset
      name: web
      namespace: web
###
###
- name: fluentd-daemonset-to-web-statefulset
  type: k8s
  protocol: tcp
  targetPort: 80
  timeoutSeconds: 67
  attempts: 3
  exitCode: 0
  src:
    k8sResource: # this is type endpoint
      kind: daemonset
      name: fluentd
      namespace: fluentd
  dst:
    k8sResource: ## this is type endpoint
      kind: statefulset
      name: web
      namespace: web
###
####
- name: busybox-deploy-to-control-plane-dot-io
  type: k8s
  protocol: tcp
  targetPort: 80
  timeoutSeconds: 67
  attempts: 3
  exitCode: 0
  src:
    k8sResource: # type endpoint
      kind: deployment
      name: busybox
      namespace: busybox
  dst:
    host: # type host or node or machine
      name: control-plane.io
###
###
- name: test-from-pod1-to-pod2
  type: k8s
  protocol: tcp
  targetPort: 80
  timeoutSeconds: 67
  attempts: 3
  exitCode: 0
  src:
    k8sResource: ##
      kind: pod
      name: pod1
      namespace: pod1
  dst:
    k8sResource:
      kind: pod
      name: pod2
      namespace: pod2
###
###
- name: busybox-deploy-to-fake-host
  type: k8s
  protocol: tcp
  targetPort: 333
  timeoutSeconds: 67
  attempts: 3
  exitCode: 1
  src:
    k8sResource: # type endpoint
      kind: deployment
      name: busybox
      namespace: busybox
  dst:
    host: # type host or node or machine
      name: 0.0.0.0
...

Components

NetAssert has three main components:

• NetAssert: This is responsible for orchestrating the tests and is also known as Netassert-Engine or simply the Engine
• NetAssertv2-packet-sniffer: This is the sniffer component that is utilised during a UDP test and is injected to the destination/target Pod as an ephemeral container
• NetAssertv2-l4-client: This is the scanner component that is injected as the scanner ephemeral container onto the source Pod and is utilised during both TCP and UDP tests

Detailed steps/flow of tests

All the tests are read from an YAML file or a directory (step 1) and the results are written following the TAP format (step 5 for UDP and step 4 for TCP). The tests are performed in two different manners depending on whether a TCP or UDP connection is used

UDP test

• Validate the test spec and ensure that the src and dst fields are correct: for udp tests both of them must be of type k8sResource
• Find a running Pod called dstPod in the object defined by the dst.k8sResource field. Ensure that the Pod is in running state and has an IP address allocated by the CNI
• Find a running Pod called srcPod in the object defined by the src.k8sResource field. Ensure that the Pod is in running state and has an IP address allocated by the CNI
• Generate a random UUID, which will be used by both ephemeral containers
• Inject the netassert-l4-client as an ephemeral container in the srcPod (step 2) and set the port and protocol according to the test specifications. Provide also the target host equal to the previously found dstPod IP address, and the random UUID that was generated in the previous step as the message to be sent over the udp connection. At the same time, inject the netassertv2-packet-sniffer (step 3) as an ephemeral container in the dstPod using the protocol, search string, number of matches and timeout defined in the test specifications. The search_string environment variable is equal to the UUID that was generated in the previous step which is expected to be found in the data sent by the scanner when the connections are successful.
• Poll that status of the ephemeral containers (step 4)
• Ensure that the netassertv2-packet-sniffer ephemeral sniffer container’s exit status matches the one defined in the test specification
• Ensure that the netassert-l4-client, exits with exit status of zero. This should always be the case as UDP is not a connection oriented protocol.

TCP test

• Validate the test spec and ensure that the src field is of type k8sResource
• Find a running Pod called srcPod in the object defined by the src.k8sResource field. Ensure that the Pod is in running state and has an IPAddress
• Check if dst has k8sResource defined as a child object. If so then find a running Pod defined by the dst.K8sResource
• Inject the netassert-l4-client as an ephemeral container in the srcPod (step 2). Configure the netassert-l4-client similarly to the udp case. If the dst field is set to host then use the host name field as the scanner target host
• Poll that status of the ephemeral containers (step 3)
• Ensure that the exit code of that container matches the exitCode field defined in the test specification

Development

• You will need Go version 1.20.x or higher. Download the latest version of just. To build the project you can use just build. The resulting binary will be in cmd/netassert/cli/netassert. To run unit tests you can use just test. There is a seperate README.md that details end-to-end testing.

Quick testing

• Make sure you have installed kind and its prerequisites

• Make sure you have also installed just

• Download the NetAssert binary from the release page

• If you want to quickly test NetAssert, you can make use of the sample test(s) and manifests provided

• You will also need a working kubernetes cluster with ephemeral/debug container support, you can spin one quickly using the justfile included in the repo

❯ just kind-down ; just kind-up

• In order to use the sample tests, you need to create kubernetes resources:

❯ just k8s-apply

  kubectl apply -f ./kubernetes/manifests
  namespace/fluentd created
  daemonset.apps/fluentd created
  namespace/echoserver created
  namespace/busybox created
  deployment.apps/echoserver created
  deployment.apps/busybox created
  namespace/web created
  statefulset.apps/web created

• Run the netassert binary pointing it to the test cases:

❯ ./netassert run --input-file cmd/netassert/cli/test-cases.yaml

❯ cat results.tap
1..4
ok 1 - busybox-deploy-to-echoserver-deploy
ok 2 - busybox-deploy-to-core-dns
ok 3 - test-from-busybox-to-web-statefulset
not ok 4 - test-from-busybox-to-host
  ---
  reason: ephemeral container netassertv2-client-u8dqy3qwo exit code for test test-from-busybox-to-host
  is 1 instead of 0
  ...

Compatibility

Netassert has been tested with the following flavours of Kubernetes:

Checking for ephemeral container support

You can check for ephemeral container support using the following command:

❯ netassert ping
2023-03-27T11:25:28.421+0100 [INFO]  [NetAssert-v2.0.0]: ✅ Successfully pinged /healthz endpoint of the Kubernetes server
2023-03-27T11:25:28.425+0100 [INFO]  [NetAssert-v2.0.0]: ✅ Ephemeral containers are supported by the Kubernetes server

Increasing logging verbosity

You can increase the logging level to debug by passing --log-level argument:

❯ netassert run --input-file ./sample-tests/test-cases/test-cases.yaml --log-level=debug

RBAC Configuration

This tool can be run according to the Principle of Least Privilege (PoLP) by properly configuring the RBAC.

The list of required permissions can be found in the netassert ClusterRole kubernetes/rbac/cluster-role.yaml, which could be redefined as a Role for namespacing reasons if needed. This role can then be bound to a "principal" either through a RoleBinding or a ClusterRoleBinding, depending on whether the scope of the role is supposed to be namespaced or not. The ClusterRoleBinding kubernetes/rbac/cluster-rolebinding.yaml is an example where the user netassert-user is assigned the role netassert using a cluster-wide binding called netassert

Limitations

• When performing UDP scanning, the sniffer container image needs cap_net_raw capability so that it can bind and read packets from the network interface. As a result, admission controllers or other security mechanisms must be modified to allow the sniffer image to run with this capability. Currenlty, the Security context used by the ephemeral sniffer container looks like the following:

...
...
   securityContext:
     allowPrivilegeEscalation: false
     capabilities:
       add:
       - NET_RAW
     runAsNonRoot: true
...
...

• Although they do not consume any resources, ephemeral containers that are injected as part of the test(s) by NetAssert will remain in the Pod specification

• Service meshes are not be currently supported

E2E Tests

• Please check this README.md