You know that feeling when you push a config change and then spend the next hour just staring at your phone, waiting for it to ring? 😅 After one too many late-night "surprises," I finally sat down and wrote a simple but strict pre-commit checklist for our Sophos XGS. It's saved my team a ton of headaches.
It's basically a Python script that runs a few sanity checks before any config is applied. It doesn't do anything fancy, just validates the basics. Here's the core logic:
```python
# pre_flight_check.py - a simple sanity checker
import re
def check_firewall_rule(rule_config):
"""Validate a single firewall rule dictionary."""
checks = []
# Ensure no ANY-ANY rules are accidentally created
if rule_config.get('source', 'Any') == 'Any' and rule_config.get('destination', 'Any') == 'Any':
checks.append("WARNING: Rule has source ANY and destination ANY.")
# Check service is specified
if rule_config.get('service') == 'Any':
checks.append("WARNING: Rule service is set to ANY.")
return checks
def validate_nat_policy(nat_config):
"""Check for common NAT misconfigurations."""
if nat_config.get('original_source') == nat_config.get('translated_source'):
return ["CRITICAL: NAT policy has identical original and translated source."]
return []
# Example usage for a batch of changes
planned_changes = load_proposed_config() # Your function here
all_warnings = []
for rule in planned_changes.get('firewall_rules', []):
all_warnings.extend(check_firewall_rule(rule))
for nat in planned_changes.get('nat_policies', []):
all_warnings.extend(validate_nat_policy(nat))
if all_warnings:
print("Hold on! Review these findings:")
for warn in all_warnings:
print(f"• {warn}")
# Optionally, exit with a non-zero code to halt automation
```
The script checks for things like:
* **ANY-ANY firewall rules** (the classic oops)
* **NAT policies** where original and translated addresses are the same
* **Missing service definitions** on critical policies
* **Duplicate object names** across zones (we got bitten by this once)
We run this in our CI pipeline now, right before any scheduled config deployment. It's not a replacement for a full test environment, but it catches the obvious blunders that can take the whole network down.
What's on your pre-change checklist? I'm always looking to add more checks. Happy coding!
Clean code, happy life
This is a fantastic habit to get into. A simple script like that can catch so many "obvious in hindsight" mistakes before they become incidents.
I'd suggest adding a check for object references, if you haven't already. A common one we see is rules that reference an address object or service group that was deleted in a previous change, leaving the rule functionally broken. A quick lookup to confirm named objects exist can save a late night.
Keep it constructive.
Object reference validation is the next logical layer, absolutely. It's the difference between checking syntax and checking semantics. Your script catches if a rule *looks* wrong; a reference check catches if a rule *is* wrong because its components are ghosts.
I'd extend that to service/port references too. A rule allowing "Prod-Web-Servers" to "Finance-DB" on "App-Service-Group" is completely invalid if that service group is empty. The rule passes a basic syntax check but does nothing.
For something like Sophos, you'd need to pull a live object list from the firewall's API or a config dump first, then cross-reference. It adds complexity, but it catches the class of error that often slips through because the rule itself is perfectly valid on the surface.
IntegrationWizard
Great approach. The script is a solid foundation. Moving from syntax validation to the semantic checks others mentioned is a logical next step, but it's important not to let perfect be the enemy of good.
If you're already parsing the config as a dictionary, consider adding a simple "null object" check first. Before you even validate the rule logic, have the script flag any rule where a key field like 'source' or 'service' has a value that's literally null, an empty string, or a string like "Deleted_Object_0x1A3". That's a quick win that catches a lot of silent failures without needing a full API integration right away.
Totally agree on the syntax vs semantics distinction. That's a really useful way to frame it.
I've seen a similar pattern play out in design systems actually. You'll have a UI component that passes every style lint and accessibility check, but it references a Figma variant or a token that's been deprecated. The rule looks perfect on paper but it's pointing at a ghost. The parallel makes me wonder if there's a general principle here: before you validate the logic, validate the *references*.
Your point about pulling a live object list from the API is spot on, but I'd add a caveat about timing. If your script grabs the object list at the start of the change window and then you apply the config an hour later, someone else could have deleted a referenced object in between. Stale checks are almost as dangerous as no checks. Any thoughts on locking the object state during the change window? That's the part that always gives me pause with cross-reference validation.