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Showing content from https://cloud.google.com/kubernetes-engine/docs/how-to/network-policy-logging below:

Use network policy logging | GKE networking

This page explains how to use network policy logging for Google Kubernetes Engine (GKE). Kubernetes network policies specify network traffic that Pods are allowed to send and receive. Network policy logging lets you record when a connection is allowed or denied by a network policy. Network policy logging can help you troubleshoot issues with network policies.

Overview

Using network policy logging, you can:

Verify that your network policies are working as expected.
Understand which Pods in your cluster are communicating with the internet.
Understand which namespaces are communicating with each other.
Recognize a Denial of Service attack.

Network policy logs are uploaded to Cloud Logging for storage, search, analysis, and alerting if Cloud Logging is enabled. Cloud Logging is enabled by default in new clusters. See Configuring logging and monitoring for GKE for more.

Requirements

Network policy logging is only available for clusters that use GKE Dataplane V2.
Network policy logging requires the Google Cloud CLI 303.0.0 or higher.
Network policy logging is not supported with Windows Server node pools.

Pricing

There are no log generation charges for network policy logging.

If you store your logs in Cloud Logging, standard Cloud Logging charges apply.

Logs can be further routed to Pub/Sub, Cloud Storage, or BigQuery. Pub/Sub, Cloud Storage, or BigQuery charges may apply. For more information, see Routing and storage overview.

Configuring network policy logging

You configure network policy logging settings by editing the NetworkLogging object in your cluster. GKE automatically creates a NetworkLogging object named default in new Dataplane V2 clusters. There can only be one NetworkLogging object per cluster and it can't be renamed.

You can configure the logging of allowed connections and the logging of denied connections separately. You can also selectively enable logging for some network policies. The following is an example of the NetworkLogging specification, with settings specified to log all allowed and denied connections:

kind: NetworkLogging
apiVersion: networking.gke.io/v1alpha1
metadata:
  name: default
spec:
  cluster:
    allow:
      log: true
      delegate: false
    deny:
      log: true
      delegate: false

Use kubectl to edit your configuration:

kubectl edit networklogging default

Note: If you use network policies to restrict traffic within Cloud Service Mesh, deploy your network policies before you activate Cloud Service Mesh in a namespace. Otherwise, long-running connections between Pods in the mesh might already have been established, and activating new network policies does not close existing connections. NetworkLogging spec

The NetworkLogging object specification is in a YAML format. This format is described in the following table:

Field Type Description cluster.allow struct Settings for logging allowed connections. Field Type Description log bool

If set to true, allowed connections in the cluster are logged; otherwise, allowed connections are not logged.

Network policies that select the Pod and have a rule that matches the connection are listed in the log message.

delegate bool

If false, all allowed connections are logged. If multiple network policies allow a connection, all matching policies are listed in the log message.

If true, allowed connections are only logged if they are allowed by a network policy with the logging annotation policy.network.gke.io/enable-logging: "true". If multiple network policies allow a connection, all matching policies with the enable-logging annotation are listed in the log message.

A configuration error occurs if you set spec.cluster.allow.delegate to true and spec.cluster.allow.log to false.

cluster.deny struct Settings for logging denied connections. Field Type Description log bool

If set to true, denied connections in the cluster are logged; otherwise, denied connections are not logged.

delegate bool

If false, all denied connections are logged.

If true, denied connections are only logged if the Pod where the connection was denied is in a namespace with the annotation policy.network.gke.io/enable-deny-logging: "true".

A configuration error occurs if you set spec.cluster.deny.delegate to true and spec.cluster.deny.log to false.

Accessing network policy logs

Network policy logs are automatically uploaded to Cloud Logging. You can access logs through the Logs Explorer or with the Google Cloud CLI. You can also route logs to a sink.

Cloud Logging

Go to the Logs Explorer page in the Google Cloud console.

Go to Logs Explorer
Click Query builder.
Use the following query to find all network policy log records:
```
resource.type="k8s_node"
resource.labels.location="CLUSTER_LOCATION"
resource.labels.cluster_name="CLUSTER_NAME"
logName="projects/PROJECT_NAME/logs/policy-action"
```
Replace the following:
- CLUSTER_LOCATION: The Compute Engine location of the cluster.
- CLUSTER_NAME: The name of your cluster.
- PROJECT_NAME: The name of your Google Cloud project.

See Using the Logs Explorer to learn how to use the Logs Explorer.

You can also build a query using the Query builder. To create a query for network policy logs, select policy-action in the Log name drop-down list. If there are no available logs, policy-action does not appear in the drop-down list.

gcloud

Find all network policy log records:

gcloud logging read --project "PROJECT_NAME" 'resource.type="k8s_node"
    resource.labels.location="CLUSTER_LOCATION"
    resource.labels.cluster_name="CLUSTER_NAME"
    logName="projects/PROJECT_NAME/logs/policy-action"'

Replace the following:

PROJECT_NAME: The name of your Google Cloud project.
CLUSTER_LOCATION: The Compute Engine location of the cluster.
CLUSTER_NAME: The name of your cluster.

You can add further conditions to filter the results. For example:

Show logs in a certain timeframe:

timestamp>="2020-06-22T06:30:51.128Z"
timestamp<="2020-06-23T06:30:51.128Z"

Show logs for denied connections:
```
jsonPayload.disposition="deny"
```

Show logs to a deployment named "redis":

jsonPayload.dest.pod_name=~"redis"
jsonPayload.dest.pod_namespace="default"

Show logs for cluster-external connections:
```
jsonPayload.dest.instance != ""
```

Show logs that match a certain network policy, in this case "allow-frontend-to-db":

jsonPayload.policies.name="allow-frontend-to-db"
jsonPayload.policies.namespace="default"

If you use a Standard cluster, you can also find the network policy logs generated on each cluster node locally at /var/log/network/policy_action.log*. A new numbered log file is created when the current log file reaches 10 MB. Up to five previous log files are stored.

Network policy log format

Network policy log records are in a JSON format. This format is described in the following table:

Field Type Description connection struct Connection information: Field Type Description src_ip string Source IP address of the connection. src_port int Source port of the connection. dest_ip string Destination IP address of the connection. dest_port int Destination port of the connection. protocol string Protocol of the connection, which can be one of tcp, udp, or icmp. direction string Direction of the connection, which can be ingress, or egress. src struct Endpoint information of the source: Field Type Description pod_name string Name of the Pod, if the source is a Pod. pod_namespace (deprecated) string Namespace of the Pod, if the source is a Pod. pod_namespace is deprecated, use namespace instead. namespace string Namespace of the Pod, if the source is a Pod. workload_name string Name of the workload, if the source workload is available. workload_kind string Kind of the workload, if the source workload is available. instance string IP address of the source, if the source is not a Pod. dest struct Endpoint information of the destination: Field Type Description pod_name string Name of the Pod, if the destination is a Pod. pod_namespace (deprecated) string Namespace of the Pod, if the destination is a Pod. pod_namespace is deprecated, use namespace instead. namespace string Namespace of the Pod, if the destination is a Pod. workload_name string Name of the workload, if the destination workload is available. workload_kind string Kind of the workload, if the destination workload is available. instance string IP address of the source, if the destination is not a Pod. disposition string Disposition of the connection, which can be allow or deny. policies list of structs

Matched policies for the allowed connections from the enforced Pod's view. For ingress connection, the enforced Pod is the destination Pod. For egress connection, the enforced Pod is the source Pod. Multiple policies are logged if a connection is matched by all of them.

This field is only included in logs of allowed connections.

Field Type Description name string Name of the matching network policy. namespace string Namespace of the matching network policy. count int Used for log aggregation of denied queries. The value is always 1 for allowed connection. node_name string The node that runs the Pod that generated this log message. timestamp string When the connection attempt occurred. Note:namespace, workload_name, and workload_kind are available in the following versions: 1.20.10-gke.2200 to 1.21 1.21.4-gke.2300 to 1.22 1.22.1-gke.1700 and later Definition of connection

For connection-oriented protocols like TCP, a log is created for each allowed or denied connection. For protocols like UDP and ICMP that aren't connection-oriented, packets are grouped into time-window based connections.

Policy logs for denied connections

The log records for denied connections don't include the policies field because the Kubernetes network policy API does not have explicit deny policies. A connection is denied if a Pod is covered by one or more network policies, but none of the policies allow the connection. This means that no policy is individually responsible for a blocked connection.

Log aggregation for denied connections

It is common for a client to retry a connection that was denied. To prevent excessive logging, repeated denied connections within a five-second window are aggregated into a single log message using the count field.

Subsequent denied connections are aggregated with a previous log message if the connection's src_ip, dest_ip, dest_port, protocol,and direction match the first denied connection. Note that the src_port of subsequent connections does not have to match because retried connections might come from a different port. The aggregated log message includes the src_prt of the first denied connection at the beginning of the aggregation window.

Example log records

The following example network policy named allow-green applied to test-service allows connections to test-service from a Pod named client-green. Implicitly, this policy denies all other ingress traffic to test-service including from the Pod client-red.

  apiVersion: networking.k8s.io/v1
  kind: NetworkPolicy
  metadata:
    name: allow-green
    namespace: default
    annotations:
      policy.network.gke.io/enable-logging: "true"
  spec:
    podSelector:
      matchLabels:
        app: test-service
    ingress:
    - from:
      - podSelector:
          matchLabels:
            app: client-green
    policyTypes:
    - Ingress

This diagram shows the effect of the allow-green policy on two connections to test-service. The allow-green policy allows the connection from client-green. Because no policy allows the connection from client-red the connection is denied.

The log for the allowed connection from client-green looks like this:

{
   "connection":{
      "src_ip":"10.84.0.252",
      "dest_ip":"10.84.0.165",
      "src_port":52648,
      "dest_port":8080,
      "protocol":"tcp",
      "direction":"ingress"
   },
   "disposition":"allow",
   "policies":[
      {
         "name":"allow-green",
         "namespace":"default"
      }
   ],
   "src":{
      "pod_name":"client-green-7b78d7c957-68mv4",
      "pod_namespace":"default",
      "namespace":"default",
      "workload_name":"client-green-7b78d7c957",
      "workload_kind":"ReplicaSet"
   },
   "dest":{
      "pod_name":"test-service-745c798fc9-sfd9h",
      "pod_namespace":"default",
      "namespace":"default",
      "workload_name":"test-service-745c798fc9",
      "workload_kind":"ReplicaSet"
   },
   "count":1,
   "node_name":"gke-demo-default-pool-5dad52ed-k0h1",
   "timestamp":"2020-06-16T03:10:37.993712906Z"
}

The log for the denied connection from client-red looks like this:

{
   "connection":{
      "src_ip":"10.84.0.180",
      "dest_ip":"10.84.0.165",
      "src_port":39610,
      "dest_port":8080,
      "protocol":"tcp",
      "direction":"ingress"
   },
   "disposition":"deny",
   "src":{
      "pod_name":"client-red-5689846f5b-b5ccx",
      "pod_namespace":"default",
      "namespace":"default",
      "workload_name":"client-red-5689846f5b",
      "workload_kind":"ReplicaSet"
   },
   "dest":{
      "pod_name":"test-service-745c798fc9-sfd9h",
      "pod_namespace":"default",
      "namespace":"default",
      "workload_name":"test-service-745c798fc9",
      "workload_kind":"ReplicaSet"
   },
   "count":3,
   "node_name":"gke-demo-default-pool-5dad52ed-k0h1",
   "timestamp":"2020-06-15T22:38:32.189649531Z"
}

Note that the denied connection log does not include the policies field. This is described in the preceding section, Policy logs for denied connections.

The denied connection log includes a count field for aggregating denied connections.

Troubleshooting issues with network policy logs

Check for error events in the NetworkLogging object:

kubectl describe networklogging default

If the logging configuration is invalid, the configuration won't take effect and an error will be reported in the events section:

Name:         default
Namespace:
Labels:       addonmanager.kubernetes.io/mode=EnsureExists
Annotations:  API Version:  networking.gke.io/v1alpha1
Kind:         NetworkLogging
Metadata:
  Creation Timestamp:  2020-06-20T05:54:08Z
  Generation:          8
  Resource Version:    187864
  Self Link:           /apis/networking.gke.io/v1alpha1/networkloggings/default
  UID:                 0f1ddd6e-4193-4295-9172-baa6a52aa6e6
Spec:
  Cluster:
    Allow:
      Delegate:  true
      Log:       false
    Deny:
      Delegate:  false
      Log:       false
Events:
  Type     Reason                 Age                From                                                               Message
  ----     ------                 ----               ----                                                               -------
  Warning  InvalidNetworkLogging  16s (x3 over 11h)  network-logging-controller, gke-anthos-default-pool-cee49209-0t09  cluster allow log action is invalid: delegate cannot be true when log is false
  Warning  InvalidNetworkLogging  16s (x3 over 11h)  network-logging-controller, gke-anthos-default-pool-cee49209-80fx  cluster allow log action is invalid: delegate cannot be true when log is false

To limit CPU utilization spent on logging, a node can log up to 500 connections per second before it starts dropping logs. The network policies on the node are still being enforced. You can see if there are dropped policy logs by checking if any error counters are incrementing:
```
kubectl exec ANETD_POD_NAME -n kube-system -- curl -s http://localhost:9990/metrics |grep policy_logging
```
Replace ANETD_POD_NAME with the name of an anetd Pod. Check each node. anetd is the networking controller for Dataplane V2.

Logs with no name appear for Pods with default deny policies

Liveness, readiness, and startup probes require that the Pod accept Ingress connections made by the probes from kubelet. To ensure that these probes function correctly, GKE automatically permits probe traffic to the selected Pod as configured for the Pod regardless of any network policies applied to the Pod. You cannot change this behavior.

Logs for probe connections are similar to the following:

{
   "connection":{
      "src_ip":"10.88.1.1",
      "dest_ip":"10.88.1.4",
      "src_port":35848,
      "dest_port":15021,
      "protocol":"tcp",
      "direction":"ingress"
   },
   "disposition":"allow",
   "src":{
      "instance":"10.88.1.1"
   },
   "dest":{
      "pod_name":"testpod-745c798fc9-sfd9h",
      "pod_namespace":"default",
      "namespace":"default",
      "workload_name":"testpod-745c798fc9",
      "workload_kind":"ReplicaSet"
   },
   "count":1,
   "policies": [
     {
       "name":""
     }
    ],
   "node_name":"gke-demo-default-pool-5dad52ed-k0h1",
   "timestamp":"2021-04-01T12:42:32.1898720941Z"
}

The log has the following characteristics:

The value of policies.name is empty because there is no associated network policy to permit the connection.
The value of connection.src_ip does not correspond to any Pods or nodes.

What's next

Learn how to view and analyze logs with Cloud Logging.
Implement common approaches to restrict traffic using network policies.

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