adminA cloud firewall controls network traffic into, out of, and between cloud resources.
Depending on the cloud platform, this may appear as security groups, network security groups, firewall rules, network ACLs, web application firewalls, or managed cloud firewalls.
The core idea is: default deny what is not needed, allow only necessary traffic, and log enough evidence to investigate incidents.
Cloud Architecture Brief
Cloud workloads can become exposed when teams open ports quickly and forget to close them later.
Companies need cloud firewalls to protect public apps, private servers, databases, admin access, and internal traffic between services.
A cloud firewall defines allowed and denied traffic using source, destination, port, protocol, identity, network tag, or application-layer rules.
If you understand source, destination, port, protocol, stateful rules, stateless rules, allowlist, denylist, and logging, you can reason about firewalls across cloud, Linux, Kubernetes, and enterprise networks.
Architecture Decision
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Internet traffic reaches a web firewall and load balancer on HTTPS. Load balancer can reach app servers on app port. App servers can reach database on database port. Admin access is restricted through VPN or bastion.
Allow traffic by architecture layer instead of opening broad public access.
Layer-based rules make traffic easier to understand, audit, and defend during incidents.
Open all ports to the internet; rely only on application passwords; allow any internal traffic; manage rules manually without naming or review.
Strict firewall rules reduce attack surface but require clearer dependency mapping. Loose rules reduce setup friction but hide dangerous exposure.
Cloud Building Blocks
Compute instances should accept traffic only from approved sources such as load balancer, bastion, VPN, or internal service ranges.
Firewall rules should match subnet design, route tables, VPN paths, private endpoints, and load balancer target groups.
Storage services should avoid public access unless intentionally serving public assets through controlled design.
Databases should accept traffic only from application security groups or controlled admin networks, never from the open internet.
Use least network access, named rule groups, WAF for HTTP threats, private admin paths, logging, and periodic rule review.
Collect firewall logs, denied traffic, accepted traffic samples, WAF events, flow logs, and alert on risky rule changes.
Enterprise Readiness
Firewall rules should not create hidden single points of failure by blocking health checks, failover traffic, or monitoring agents.
Use reusable rule groups, tags, and infrastructure as code so rules scale across environments.
Block 0.0.0.0/0 on admin ports, restrict database ports, use WAF for public HTTP apps, and alert on public exposure changes.
Use the right firewall layer. Do not send all traffic through expensive appliances when native security groups or WAF rules are enough.
When traffic is blocked, check source, destination, port, protocol, route path, security group, network ACL, WAF rule, and application listener.
Failure & Job Readiness
Open SSH or RDP to the world, database port public, missing health check allow rule, overlapping rules, no logs, and emergency rules never removed.
Confirm no public admin ports; confirm database is private; confirm WAF for public app if needed; confirm logs; confirm rule owner and reason.
Remove risky public rules, restore previous firewall version, isolate compromised instance, allow required health check, and document rule change.
A company wants a public web application but must keep admin access and database traffic private and auditable.
Explain the difference between network firewall rules, security groups, and web application firewall controls.
Create a rule matrix: internet to load balancer, load balancer to app, app to database, admin to bastion, monitoring to servers. Deny everything else.
VPC; Security Group; WAF; Network ACL; Zero Trust; Bastion Host