Introduction:

In the world of Kubernetes (K8s), security is of utmost importance. Two key components for ensuring the security of your applications are external firewall and web application firewall (WAF). In this article, we will guide you through the process of implementing external firewall and web application firewall in Kubernetes.

Steps to Implement External Firewall and Web Application Firewall in Kubernetes:

| Step | Description |
|------|-------------|
| 1. | Deploying an External Firewall Network Policy |
| 2. | Setting up a Web Application Firewall (WAF) |

Step 1: Deploying an External Firewall Network Policy

In Kubernetes, Network Policies are used to control the traffic flow between pods. External firewall rules can be enforced using Network Policies. Here's how you can deploy a Network Policy for an external firewall:

```yaml
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
name: external-firewall-policy
spec:
podSelector:
matchLabels: {}
policyTypes:
- Egress
egress:
- to:
- ipBlock:
cidr: 0.0.0.0/0
except:
- 192.168.0.0/16
- 10.0.0.0/8
ports:
- protocol: TCP
port: 80
```

Explanation of the code:
- `metadata`: Specifies the name of the Network Policy.
- `podSelector`: Defines which pods the Network Policy applies to.
- `policyTypes`: Specifies the type of policy (egress in this case).
- `egress`: Defines the egress rules for the policy.
- `ipBlock`: Specifies the CIDR range that the traffic is allowed to egress to.
- `except`: Exempts specific IP ranges from the rule.
- `ports`: Defines the ports that are allowed for egress traffic.

Step 2: Setting up a Web Application Firewall (WAF)

A WAF is used to protect web applications from various attacks such as SQL injection, cross-site scripting, etc. There are various tools available for deploying a WAF in Kubernetes. One popular tool is ModSecurity, which is an open-source WAF.

Here's how you can deploy ModSecurity as a WAF in Kubernetes:

```yaml
apiVersion: apps/v1
kind: Deployment
metadata:
name: modsecurity-waf
spec:
replicas: 1
selector:
matchLabels:
app: modsecurity-waf
template:
metadata:
labels:
app: modsecurity-waf
spec:
containers:
- name: modsecurity
image: owasp/modsecurity-crs:latest
ports:
- containerPort: 80
```

Explanation of the code:
- `metadata`: Specifies the name of the Deployment.
- `replicas`: Defines the number of replicas for the Deployment.
- `selector`: Defines the labels used to select pods to manage.
- `template`: Specifies the pod template.
- `containers`: Defines the containers to run in the pod.
- `name`: Specifies the name of the container.
- `image`: Specifies the Docker image to use for the container (ModSecurity CRS).
- `ports`: Defines the ports to expose on the container.

Conclusion:

By following the steps outlined in this article, you can implement external firewall and web application firewall in Kubernetes to enhance the security of your applications. Remember that security is an ongoing process, and it is important to regularly update your firewall rules and WAF to protect your applications from new threats.