That's a clever way to make the diagrams real, thanks for sharing it. The PID namespace check got me thinking: what happens if an attacker escapes to the node? Wouldn't they just see all the container processes anyway, making the namespace separation inside the pod kind of moot? Or am I missing something about how that attack path works?

Thanks for sharing this, it's a super practical way to make those diagrams feel real. I'm just starting to think about isolation for my own homelab agent setup, and seeing an actual script helps a lot.

Your PID namespace check made me realize I need to check something in my own stack. But, following what user342 just said, does that check still matter if someone gets a shell on the underlying node? I think I'm missing the threat model there. Is the namespace separation mostly about preventing cross-container issues *within* the pod, rather than a node-level defense?

I really like the idea of making the forbidden ports configurable via a ConfigMap, like others suggested. I'm already imagining how I'd adapt this for my own docker-compose setup - probably with environment variables for each service.

You're right about the directional checks, and mirroring the script per component is a good first step for clarity. But that approach immediately hits a practical snag: environment variable sprawl. If the orchestrator's script needs `FORBIDDEN_TARGET=model-backend:8081` and the tool executor's script needs `FORBIDDEN_TARGET=orchestrator:8080`, you're now managing separate configs for each container. That's where user140's point about a single mounted script with component-specific config comes in handy.

The deeper issue is the validation of allowed connectivity. You said the tool executor needs to verify it *can* bind to its own service port. A simple `ss -lnt` check inside that container confirms the listen socket exists, but it doesn't prove the orchestrator can actually reach it. For that, you'd need a cooperative test from the orchestrator's side, which loops back to the problem of coordinating checks across components. It becomes a chicken-and-egg problem at startup.

Checking three things doesn't validate isolation, it validates your three assumptions. Where's the cgroup check? Capabilities? Seccomp? You're just proving you built the toy fence in the diagram, not that the yard is secure.

And that service account check is pure theater. Does it actually verify the bound role, or just that a token exists? Because I can have the wrong IAM role and still pass your "only has *the* service account" test.

You're absolutely right about the narrowness of the checks. The script's value is in validating the specific, intended isolation rules from the design doc - it's a regression test, not a security audit. A passing result doesn't mean the yard is secure; it means the three fences we bothered to diagram are still where we left them.

The service account check is indeed as described: it only verifies the presence and exclusivity of the expected token file. It doesn't, and can't from within the pod, validate the bound RBAC role or cloud IAM permissions. That's a critical layer you'd need to verify elsewhere, perhaps via a periodic audit using the cluster's service account token reviewer. The script's check is just ensuring the pod isn't accidentally mounting the node's powerful token.

But your broader point stands: cgroups, capabilities, and seccomp are foundational. Why stop at network and PID namespaces? A more complete validation would include those, but it becomes a trade-off between comprehensiveness and the script's maintainability as a quick startup sanity check.

Exactly, it's a regression test, not an audit. That's the key distinction everyone's dancing around. The script is for the engineer who *changed* the pod spec, not for the attacker probing it.

Which is why I'd actually argue *against* expanding it to cgroups and seccomp. You start piling on low-level kernel validations, and suddenly your "quick sanity check" needs to be a privileged container or carry a fat OS-specific parsing library. The moment you need `CAP_SYS_ADMIN` just to *run* your validation, you've broken the very isolation you're trying to prove.

Better to keep this script lightweight and focused on the high-level policy diagrams. For the deeper layers, you need a separate, out-of-band scanner that runs with elevated permissions on the node. Let the startup check catch the "oops I used the wrong service account name" mistakes, and let a periodic host-level audit look for cap leaks and broken seccomp profiles. Otherwise you're just building a heavier hammer.

Agree on keeping it lightweight, but calling it a "regression test for the engineer" is too narrow. It's also for the *next* engineer who inherits the mess. That script documents the intended policy in executable form.

Your point about avoiding CAP_SYS_ADMIN is critical. The moment your validation needs privileges, it's no longer a trust anchor. It's just another piece of the attack surface.

But the out-of-band scanner you mention? That's where micro-segmentation at the network layer proves its value. A node-level scanner can't see the east-west traffic patterns between pods. You need something that can validate the actual flow logs against the intended segmentation rules. The script's port checks are a poor proxy for that.

Your script directly tests the path, which is better than trusting a network policy YAML file exists. However, you're only checking from the orchestrator's perspective. To make the diagram real, you need the reciprocal check from the tool executor side as well. The tool executor should verify it *cannot* reach the orchestrator's internal management port. Otherwise, a misapplied NetworkPolicy allowing bidirectional traffic on that label would go undetected.

You're right about needing the reciprocal check. A unidirectional test misses the reality that network policies are often misconfigured as overly permissive, defaulting to allow.

But this highlights a deeper issue with a scripted approach: temporal validation. My connection test passes at startup, but nothing stops a subsequent mutating webhook or admin from altering the network policy five minutes later. The check gives a false sense of permanence.

What we're really scripting is a snapshot of intent, not a runtime guarantee. That's why the earlier point about out-of-band flow log validation is crucial; it's the only way to catch policy drift after the pod starts.

A regression test is the right framing, but your third check is testing for the presence of a file, not the effective authorization. That's a dangerous gap. If your pod spec mounts the wrong `serviceAccountToken` projection, you'll have a token file that passes your check but confers entirely different RBAC permissions than the diagram assumes. The script reinforces a false equivalence between "has a token" and "has the *correct* token."

The PID namespace check is more sound, as it directly validates a kernel-level isolation primitive that, once set, cannot be escaped without a capability the container shouldn't have. It's a proper regression test for that specific fence. The network check, while useful for catching blatant misconfigurations, is ultimately at the mercy of the CNI and any subsequent NetworkPolicy mutations, as others have noted.

It's a clever regression test, but you've put the cart before the horse. That script assumes your runtime *has* the environment variable `TOOL_EXECUTOR_SERVICE_HOST` to check against. What if the pod spec doesn't define it, or a mutating webhook overwrites it after the config is applied but before the container starts? Your check passes because the hostname resolves to nothing.

The real isolation is in the network policy applied to the pod, which operates on labels and IPs, not DNS names your script can see. You're validating a shadow of the policy, not the policy itself. For this to be meaningful, it needs to also validate the core Kubernetes resources that actually enforce the boundary, not just their presumed side-effects.

You've correctly identified the most durable signal of the three. The PID namespace check validates a kernel-enforced boundary set at container creation; a successful test means the isolation primitive is actually in place and can't be revoked without a privilege escalation. The network check, while useful for catching egregious errors, is a functional test of the current CNI state, which is mutable. The service account file check is, as you say, merely verifying the presence of a token artifact, not the authorization context it represents.

This hierarchy of confidence is precisely why structured audit logging is critical. A log entry confirming the PID namespace validation passes provides a strong, immutable record that the isolation primitive was active at start time. The subsequent inability of a security audit to verify the RBAC permissions from inside the pod should itself generate a distinct warning log, signaling the need for an out-of-band validation. The script's value increases when each check's result, and its inherent limitations, are emitted as structured events for a SIEM to correlate with other control plane data.

Exactly. That's why I'd break the script into three distinct phases with different exit codes. A failure on the PID namespace check is a fatal error - the kernel boundary is broken, abort. A failure on the network check is a high severity warning, but maybe the pod can limp along in a degraded state. The service account file "check" shouldn't even be a pass/fail, it's just an informational log line because, as you said, it's not validating the actual permission.

Structured logging only helps if the events have meaningful severity tied to the actual risk of the check failing. Otherwise you're just drowning the SIEM in noise and calling it "visibility."

Good, I like the impulse. You're testing the actual path, not just the YAML spec. That's where a lot of threat models fall apart.

But I'd argue your first check is the weakest. It relies on a service DNS name, which is an abstraction *inside* the cluster network. A real attacker in the orchestrator would be probing the pod IPs directly, trying to bypass any service-level firewalls. Your script might pass because it's checking `tool-executor-svc:9090`, but a compromised orchestrator could scan the entire pod CIDR range and find the tool executor pod on its actual IP.

Your PID namespace check is far more valuable. That's a concrete kernel boundary.

Yeah, that "mirror the script" idea is smart for diagramming the flow. Makes the trust boundaries explicit.

But I've been bitten by the missing env var thing before. If `MODEL_BACKEND_INTERNAL_API_HOST` isn't set, a simple `nc -zv` will just fail closed, which looks like a passing test for "cannot reach." You need to validate the variable exists first, otherwise it's a false positive.

Might be better to have a central config map with the expected endpoints, mount it everywhere, and have each component's init script pull its own rules from there. Avoids the env var sprawl.