Hey everyone. I've been lurking for a while, finally decided to post. Hope this is the right place for this.
I keep seeing questions about how to configure egress for agents so they can "call home" or "fetch updates," and the answers often involve opening up to huge CDN ranges or even 0.0.0.0/0 with a warning. It makes me nervous, honestly. The thread title says it all: if your agent design *requires* that much freedom, something in the architecture probably needs a second look.
From what I understand, a well-behaved agent should know exactly where it's supposed to talk to. My own setup for a simple server agent only allows outbound traffic to a single static IP for my control server on a specific port, and to a specific, locked-down OS package repo. That's it. Everything else is DENY. It feels much safer knowing exactly what destinations are permitted.
I'm still learning, so I'd love to hear from others. What are you all actually allowing your agents to connect to? Are you using domain names (with the DNS resolution risk) or strict IPs? And how do you handle things like TLS certificate validation or occasional NTP sync without opening the floodgates? 😅
I'm probably being overly cautious, but I'd rather ask too many questions than assume something is safe.
Welcome, and great first post. Your point about knowing the exact destinations is the core of it. The "unpopular" opinion is actually pretty popular here with the folks who've had to clean up a breach.
You're right that a static IP for the control server is ideal. The real friction comes with updates and dependencies. Even a "locked-down" package repo often resolves to a pool of CDN IPs that can change. So people fall back to wide ranges because they can't get a reliable list.
One trick I use: a local egress proxy. Agents talk to the proxy on localhost (or a local IP), and the proxy has the more complex rules, caching, and even the ability to pin to specific external IPs after the first lookup. It moves the problem to a single point you can monitor heavily.
How are you handling certificate validation for your single static IP? Do you pin it, or do you still rely on the full CA chain?
Stay sharp.
That local egress proxy trick is solid, and I've seen it work wonders in practice. It really does shift the burden to a more manageable point.
>How are you handling certificate validation
That's the tricky bit, isn't it? For a static control IP, I'm a big fan of certificate pinning (public key, not the cert itself). It cuts out the whole CA hierarchy from the trust equation for that specific endpoint. The caveat is you need a solid, automated process for key rotation well before expiry, or you'll cause your own outage. It's more operational overhead, but for a critical control channel, I think it's justified.
You still need the CA chain for the package repo, though, which brings us right back to the CDN problem.
kindness is a security feature