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Chapter 3. Network policies
3.1. About network policies Copiar enlaceEnlace copiado en el portapapeles!
Learn how network policies work for MicroShift to restrict or allow network traffic to pods in your cluster.
3.1.1. How network policy works in MicroShift Copiar enlaceEnlace copiado en el portapapeles!
In a cluster using the default OVN-Kubernetes Container Network Interface (CNI) plugin for MicroShift, network isolation is controlled by both firewalld, which is configured on the host, and by NetworkPolicy objects created within MicroShift. Simultaneous use of firewalld and NetworkPolicy is supported.
-
Network policies work only within boundaries of OVN-Kubernetes-controlled traffic, so they can apply to every situation except for
hostPort/hostNetworkenabled pods. -
Firewalld settings also do not apply to
hostPort/hostNetworkenabled pods.
Firewalld rules run before any NetworkPolicy is enforced.
Network policy does not apply to the host network namespace. Pods with host networking enabled are unaffected by network policy rules. However, pods connecting to the host-networked pods might be affected by the network policy rules.
Network policies cannot block traffic from localhost.
By default, all pods in a MicroShift node are accessible from other pods and network endpoints. To isolate one or more pods in a cluster, you can create NetworkPolicy objects to indicate allowed incoming connections. You can create and delete NetworkPolicy objects.
If a pod is matched by selectors in one or more NetworkPolicy objects, then the pod accepts only connections that are allowed by at least one of those NetworkPolicy objects. A pod that is not selected by any NetworkPolicy objects is fully accessible.
A network policy applies to only the TCP, UDP, ICMP, and SCTP protocols. Other protocols are not affected.
The following example NetworkPolicy objects demonstrate supporting different scenarios:
Deny all traffic:
To make a project deny by default, add a
NetworkPolicyobject that matches all pods but accepts no traffic:Copy to Clipboard Copied! Toggle word wrap Toggle overflow Allow connections from the default router, which is the ingress in MicroShift:
To allow connections from the MicroShift default router, add the following
NetworkPolicyobject:Copy to Clipboard Copied! Toggle word wrap Toggle overflow Only accept connections from pods within the same namespace:
To make pods accept connections from other pods in the same namespace, but reject all other connections from pods in other namespaces, add the following
NetworkPolicyobject:Copy to Clipboard Copied! Toggle word wrap Toggle overflow Only allow HTTP and HTTPS traffic based on pod labels:
To enable only HTTP and HTTPS access to the pods with a specific label (
role=frontendin following example), add aNetworkPolicyobject similar to the following:Copy to Clipboard Copied! Toggle word wrap Toggle overflow Accept connections by using both namespace and pod selectors:
To match network traffic by combining namespace and pod selectors, you can use a
NetworkPolicyobject similar to the following:Copy to Clipboard Copied! Toggle word wrap Toggle overflow
NetworkPolicy objects are additive, which means you can combine multiple NetworkPolicy objects together to satisfy complex network requirements.
For example, for the NetworkPolicy objects defined in previous examples, you can define both allow-same-namespace and allow-http-and-https policies. That configuration allows the pods with the label role=frontend to accept any connection allowed by each policy. That is, connections on any port from pods in the same namespace, and connections on ports 80 and 443 from pods in any namespace.
3.1.2. Optimizations for network policy with OVN-Kubernetes network plugin Copiar enlaceEnlace copiado en el portapapeles!
When designing your network policy, refer to the following guidelines:
-
For network policies with the same
spec.podSelectorspec, it is more efficient to use one network policy with multipleingressoregressrules, than multiple network policies with subsets ofingressoregressrules. Every
ingressoregressrule based on thepodSelectorornamespaceSelectorspec generates the number of OVS flows proportional tonumber of pods selected by network policy + number of pods selected by ingress or egress rule. Therefore, it is preferable to use thepodSelectorornamespaceSelectorspec that can select as many pods as you need in one rule, instead of creating individual rules for every pod.For example, the following policy contains two rules:
Copy to Clipboard Copied! Toggle word wrap Toggle overflow The following policy expresses those same two rules as one:
Copy to Clipboard Copied! Toggle word wrap Toggle overflow The same guideline applies to the
spec.podSelectorspec. If you have the sameingressoregressrules for different network policies, it might be more efficient to create one network policy with a commonspec.podSelectorspec. For example, the following two policies have different rules:Copy to Clipboard Copied! Toggle word wrap Toggle overflow The following network policy expresses those same two rules as one:
Copy to Clipboard Copied! Toggle word wrap Toggle overflow You can apply this optimization when only multiple selectors are expressed as one. In cases where selectors are based on different labels, it may not be possible to apply this optimization. In those cases, consider applying some new labels for network policy optimization specifically.
3.1.2.1. NetworkPolicy CR and external IPs in OVN-Kubernetes Copiar enlaceEnlace copiado en el portapapeles!
In OVN-Kubernetes, the NetworkPolicy custom resource (CR) enforces strict isolation rules. If a service is exposed using an external IP, a network policy can block access from other namespaces unless explicitly configured to allow traffic.
To allow access to external IPs across namespaces, create a NetworkPolicy CR that explicitly permits ingress from the required namespaces and ensures traffic is allowed to the designated service ports. Without allowing traffic to the required ports, access might still be restricted.
Example output
where:
<policy_name>- Specifies your name for the policy.
<my_namespace>- Specifies the name of the namespace where the policy is deployed.
For more details, see "About network policy".
3.2. Creating network policies Copiar enlaceEnlace copiado en el portapapeles!
You can create a network policy for a namespace.
3.2.1. Example NetworkPolicy object Copiar enlaceEnlace copiado en el portapapeles!
The following annotates an example NetworkPolicy object:
- 1
- The name of the NetworkPolicy object.
- 2
- A selector that describes the pods to which the policy applies.
- 3
- A selector that matches the pods from which the policy object allows ingress traffic. The selector matches pods in the same namespace as the NetworkPolicy.
- 4
- A list of one or more destination ports on which to accept traffic.
3.2.2. Creating a network policy using the CLI Copiar enlaceEnlace copiado en el portapapeles!
To define granular rules describing ingress or egress network traffic allowed for namespaces in your cluster, you can create a network policy.
Prerequisites
-
You installed the OpenShift CLI (
oc). - You are working in the namespace that the network policy applies to.
Procedure
Create a policy rule:
Create a
<policy_name>.yamlfile:touch <policy_name>.yaml
$ touch <policy_name>.yamlCopy to Clipboard Copied! Toggle word wrap Toggle overflow where:
<policy_name>- Specifies the network policy file name.
Define a network policy in the file that you just created, such as in the following examples:
Deny ingress from all pods in all namespaces
This is a fundamental policy, blocking all cross-pod networking other than cross-pod traffic allowed by the configuration of other Network Policies.
Copy to Clipboard Copied! Toggle word wrap Toggle overflow Allow ingress from all pods in the same namespace
Copy to Clipboard Copied! Toggle word wrap Toggle overflow Allow ingress traffic to one pod from a particular namespace
This policy allows traffic to pods labelled
pod-afrom pods running innamespace-y.Copy to Clipboard Copied! Toggle word wrap Toggle overflow
To create the network policy object, enter the following command:
oc apply -f <policy_name>.yaml -n <namespace>
$ oc apply -f <policy_name>.yaml -n <namespace>Copy to Clipboard Copied! Toggle word wrap Toggle overflow where:
<policy_name>- Specifies the network policy file name.
<namespace>- Optional: Specifies the namespace if the object is defined in a different namespace than the current namespace.
Example output
networkpolicy.networking.k8s.io/deny-by-default created
networkpolicy.networking.k8s.io/deny-by-default createdCopy to Clipboard Copied! Toggle word wrap Toggle overflow
3.2.3. Creating a default deny all network policy Copiar enlaceEnlace copiado en el portapapeles!
This is a fundamental policy, blocking all cross-pod networking other than network traffic allowed by the configuration of other deployed network policies. This procedure enforces a default deny-by-default policy.
Prerequisites
-
You installed the OpenShift CLI (
oc). - You are working in the namespace that the network policy applies to.
Procedure
Create the following YAML that defines a
deny-by-defaultpolicy to deny ingress from all pods in all namespaces. Save the YAML in thedeny-by-default.yamlfile:Copy to Clipboard Copied! Toggle word wrap Toggle overflow Apply the policy by entering the following command:
oc apply -f deny-by-default.yaml
$ oc apply -f deny-by-default.yamlCopy to Clipboard Copied! Toggle word wrap Toggle overflow Example output
networkpolicy.networking.k8s.io/deny-by-default created
networkpolicy.networking.k8s.io/deny-by-default createdCopy to Clipboard Copied! Toggle word wrap Toggle overflow
3.2.4. Creating a network policy to allow traffic from external clients Copiar enlaceEnlace copiado en el portapapeles!
With the deny-by-default policy in place you can proceed to configure a policy that allows traffic from external clients to a pod with the label app=web.
Firewalld rules run before any NetworkPolicy is enforced.
Follow this procedure to configure a policy that allows external service from the public Internet directly or by using a Load Balancer to access the pod. Traffic is only allowed to a pod with the label app=web.
Prerequisites
-
You installed the OpenShift CLI (
oc). - You are working in the namespace that the network policy applies to.
Procedure
Create a policy that allows traffic from the public Internet directly or by using a load balancer to access the pod. Save the YAML in the
web-allow-external.yamlfile:Copy to Clipboard Copied! Toggle word wrap Toggle overflow Apply the policy by entering the following command:
oc apply -f web-allow-external.yaml
$ oc apply -f web-allow-external.yamlCopy to Clipboard Copied! Toggle word wrap Toggle overflow Example output
networkpolicy.networking.k8s.io/web-allow-external created
networkpolicy.networking.k8s.io/web-allow-external createdCopy to Clipboard Copied! Toggle word wrap Toggle overflow
3.2.5. Creating a network policy allowing traffic to an application from all namespaces Copiar enlaceEnlace copiado en el portapapeles!
Follow this procedure to configure a policy that allows traffic from all pods in all namespaces to a particular application.
Prerequisites
-
You installed the OpenShift CLI (
oc). - You are working in the namespace that the network policy applies to.
Procedure
Create a policy that allows traffic from all pods in all namespaces to a particular application. Save the YAML in the
web-allow-all-namespaces.yamlfile:Copy to Clipboard Copied! Toggle word wrap Toggle overflow NoteBy default, if you omit specifying a
namespaceSelectorit does not select any namespaces, which means the policy allows traffic only from the namespace the network policy is deployed to.Apply the policy by entering the following command:
oc apply -f web-allow-all-namespaces.yaml
$ oc apply -f web-allow-all-namespaces.yamlCopy to Clipboard Copied! Toggle word wrap Toggle overflow Example output
networkpolicy.networking.k8s.io/web-allow-all-namespaces created
networkpolicy.networking.k8s.io/web-allow-all-namespaces createdCopy to Clipboard Copied! Toggle word wrap Toggle overflow
Verification
Start a web service in the
defaultnamespace by entering the following command:oc run web --namespace=default --image=nginx --labels="app=web" --expose --port=80
$ oc run web --namespace=default --image=nginx --labels="app=web" --expose --port=80Copy to Clipboard Copied! Toggle word wrap Toggle overflow Run the following command to deploy an
alpineimage in thesecondarynamespace and to start a shell:oc run test-$RANDOM --namespace=secondary --rm -i -t --image=alpine -- sh
$ oc run test-$RANDOM --namespace=secondary --rm -i -t --image=alpine -- shCopy to Clipboard Copied! Toggle word wrap Toggle overflow Run the following command in the shell and observe that the request is allowed:
wget -qO- --timeout=2 http://web.default
# wget -qO- --timeout=2 http://web.defaultCopy to Clipboard Copied! Toggle word wrap Toggle overflow Expected output
Copy to Clipboard Copied! Toggle word wrap Toggle overflow
3.2.6. Creating a network policy allowing traffic to an application from a namespace Copiar enlaceEnlace copiado en el portapapeles!
Follow this procedure to configure a policy that allows traffic to a pod with the label app=web from a particular namespace. You might want to do this to:
- Restrict traffic to a production database only to namespaces where production workloads are deployed.
- Enable monitoring tools deployed to a particular namespace to scrape metrics from the current namespace.
Prerequisites
-
You installed the OpenShift CLI (
oc). - You are working in the namespace that the network policy applies to.
Procedure
Create a policy that allows traffic from all pods in a particular namespaces with a label
purpose=production. Save the YAML in theweb-allow-prod.yamlfile:Copy to Clipboard Copied! Toggle word wrap Toggle overflow Apply the policy by entering the following command:
oc apply -f web-allow-prod.yaml
$ oc apply -f web-allow-prod.yamlCopy to Clipboard Copied! Toggle word wrap Toggle overflow Example output
networkpolicy.networking.k8s.io/web-allow-prod created
networkpolicy.networking.k8s.io/web-allow-prod createdCopy to Clipboard Copied! Toggle word wrap Toggle overflow
Verification
Start a web service in the
defaultnamespace by entering the following command:oc run web --namespace=default --image=nginx --labels="app=web" --expose --port=80
$ oc run web --namespace=default --image=nginx --labels="app=web" --expose --port=80Copy to Clipboard Copied! Toggle word wrap Toggle overflow Run the following command to create the
prodnamespace:oc create namespace prod
$ oc create namespace prodCopy to Clipboard Copied! Toggle word wrap Toggle overflow Run the following command to label the
prodnamespace:oc label namespace/prod purpose=production
$ oc label namespace/prod purpose=productionCopy to Clipboard Copied! Toggle word wrap Toggle overflow Run the following command to create the
devnamespace:oc create namespace dev
$ oc create namespace devCopy to Clipboard Copied! Toggle word wrap Toggle overflow Run the following command to label the
devnamespace:oc label namespace/dev purpose=testing
$ oc label namespace/dev purpose=testingCopy to Clipboard Copied! Toggle word wrap Toggle overflow Run the following command to deploy an
alpineimage in thedevnamespace and to start a shell:oc run test-$RANDOM --namespace=dev --rm -i -t --image=alpine -- sh
$ oc run test-$RANDOM --namespace=dev --rm -i -t --image=alpine -- shCopy to Clipboard Copied! Toggle word wrap Toggle overflow Run the following command in the shell and observe that the request is blocked:
wget -qO- --timeout=2 http://web.default
# wget -qO- --timeout=2 http://web.defaultCopy to Clipboard Copied! Toggle word wrap Toggle overflow Expected output
wget: download timed out
wget: download timed outCopy to Clipboard Copied! Toggle word wrap Toggle overflow Run the following command to deploy an
alpineimage in theprodnamespace and start a shell:oc run test-$RANDOM --namespace=prod --rm -i -t --image=alpine -- sh
$ oc run test-$RANDOM --namespace=prod --rm -i -t --image=alpine -- shCopy to Clipboard Copied! Toggle word wrap Toggle overflow Run the following command in the shell and observe that the request is allowed:
wget -qO- --timeout=2 http://web.default
# wget -qO- --timeout=2 http://web.defaultCopy to Clipboard Copied! Toggle word wrap Toggle overflow Expected output
Copy to Clipboard Copied! Toggle word wrap Toggle overflow
3.3. Editing a network policy Copiar enlaceEnlace copiado en el portapapeles!
You can edit an existing network policy for a namespace. Typical edits might include changes to the pods to which the policy applies, allowed ingress traffic, and the destination ports on which to accept traffic. The apiVersion, kind, and name fields must not be changed when editing NetworkPolicy objects, as these define the resource itself.
3.3.1. Editing a network policy Copiar enlaceEnlace copiado en el portapapeles!
You can edit a network policy in a namespace.
Prerequisites
-
You installed the OpenShift CLI (
oc). - You are working in the namespace where the network policy exists.
Procedure
Optional: To list the network policy objects in a namespace, enter the following command:
oc get networkpolicy
$ oc get networkpolicyCopy to Clipboard Copied! Toggle word wrap Toggle overflow where:
<namespace>- Optional: Specifies the namespace if the object is defined in a different namespace than the current namespace.
Edit the network policy object.
If you saved the network policy definition in a file, edit the file and make any necessary changes, and then enter the following command.
oc apply -n <namespace> -f <policy_file>.yaml
$ oc apply -n <namespace> -f <policy_file>.yamlCopy to Clipboard Copied! Toggle word wrap Toggle overflow where:
<namespace>- Optional: Specifies the namespace if the object is defined in a different namespace than the current namespace.
<policy_file>- Specifies the name of the file containing the network policy.
If you need to update the network policy object directly, enter the following command:
oc edit networkpolicy <policy_name> -n <namespace>
$ oc edit networkpolicy <policy_name> -n <namespace>Copy to Clipboard Copied! Toggle word wrap Toggle overflow where:
<policy_name>- Specifies the name of the network policy.
<namespace>- Optional: Specifies the namespace if the object is defined in a different namespace than the current namespace.
Confirm that the network policy object is updated.
oc describe networkpolicy <policy_name> -n <namespace>
$ oc describe networkpolicy <policy_name> -n <namespace>Copy to Clipboard Copied! Toggle word wrap Toggle overflow where:
<policy_name>- Specifies the name of the network policy.
<namespace>- Optional: Specifies the namespace if the object is defined in a different namespace than the current namespace.
3.3.2. Example NetworkPolicy object Copiar enlaceEnlace copiado en el portapapeles!
The following annotates an example NetworkPolicy object:
- 1
- The name of the NetworkPolicy object.
- 2
- A selector that describes the pods to which the policy applies.
- 3
- A selector that matches the pods from which the policy object allows ingress traffic. The selector matches pods in the same namespace as the NetworkPolicy.
- 4
- A list of one or more destination ports on which to accept traffic.
3.4. Deleting a network policy Copiar enlaceEnlace copiado en el portapapeles!
You can delete a network policy from a namespace.
3.4.1. Deleting a network policy using the CLI Copiar enlaceEnlace copiado en el portapapeles!
You can delete a network policy in a namespace.
Prerequisites
-
You installed the OpenShift CLI (
oc). - You are working in the namespace where the network policy exists.
Procedure
To delete a network policy object, enter the following command:
oc delete networkpolicy <policy_name> -n <namespace>
$ oc delete networkpolicy <policy_name> -n <namespace>Copy to Clipboard Copied! Toggle word wrap Toggle overflow where:
<policy_name>- Specifies the name of the network policy.
<namespace>- Optional: Specifies the namespace if the object is defined in a different namespace than the current namespace.
Example output
networkpolicy.networking.k8s.io/default-deny deleted
networkpolicy.networking.k8s.io/default-deny deletedCopy to Clipboard Copied! Toggle word wrap Toggle overflow
3.5. Viewing a network policy Copiar enlaceEnlace copiado en el portapapeles!
Use the following procedure to view a network policy for a namespace.
3.5.1. Viewing network policies using the CLI Copiar enlaceEnlace copiado en el portapapeles!
You can examine the network policies in a namespace.
Prerequisites
-
You installed the OpenShift CLI (
oc). - You are working in the namespace where the network policy exists.
Procedure
List network policies in a namespace:
To view network policy objects defined in a namespace, enter the following command:
oc get networkpolicy
$ oc get networkpolicyCopy to Clipboard Copied! Toggle word wrap Toggle overflow Optional: To examine a specific network policy, enter the following command:
oc describe networkpolicy <policy_name> -n <namespace>
$ oc describe networkpolicy <policy_name> -n <namespace>Copy to Clipboard Copied! Toggle word wrap Toggle overflow where:
<policy_name>- Specifies the name of the network policy to inspect.
<namespace>- Optional: Specifies the namespace if the object is defined in a different namespace than the current namespace.
For example:
oc describe networkpolicy allow-same-namespace
$ oc describe networkpolicy allow-same-namespaceCopy to Clipboard Copied! Toggle word wrap Toggle overflow Output for
oc describecommandCopy to Clipboard Copied! Toggle word wrap Toggle overflow