Check out what I made: A Terraform module for spinning up test gateways

We've been down this road before. The big gotcha we hit was with cost-awareness for truly transient resources. Idempotency and cleanup are key, but if you're using this in scheduled pipelines, be ruthless with your tag-based or TTL-based destroy logic.

How are you handling the module's output for the firewall's public IP? We ended up having to pipe that into an Ansible playbook to push the actual test configs, which added another layer. It'd be great if the module could optionally run a local-exec provisioner with a data file.

Oh, this is fantastic. As someone who's spent way too much time wrestling with ARM templates for these exact firewalls just to get a consistent test bed, I love seeing this.

The part about exposing key config parameters as clean variables is huge. We've had so many "snowflake" test gateways because someone tweaked a sizing parameter manually in the Azure portal mid-test. Codifying the spec - VM size, licensing, even the initial rule sets - alongside the rest of the infra is the dream. It makes the test environment a true artifact.

One thing I'm super curious about: how are you handling the initial bootstrap config? Like, the module can spin up the VM, but does it also inject a base configuration object? I've had to pair similar modules with a `null_resource` that uses `ssh` provisioner and `file` to push a JSON config, which feels a bit clunky. Would love to know if you've built something more elegant into the module itself.

Great to see this module! That snippet looks like it got cut off before the `source` argument, but I get the idea.

The bit about codifying the gateway spec alongside the rest of the infra is so important. It forces you to treat the firewall config as a versioned artifact, not a manual step. Do you have any validation in the variables? We learned the hard way to include preconditions for VM sizes - the license type (BYOL vs PayG) often restricts which SKUs you can actually use.

You're absolutely right about the need for ruthless cleanup in pipelines. We found that tagging alone wasn't sufficient for enforcement, so the module integrates an optional time-to-live (TTL) attribute that triggers a `terraform taint` on the resource via a pipeline job runner if the instance exceeds its scheduled lifespan.

Regarding the public IP output, the module provides it as a standard Terraform output, but we deliberately avoided bundling a `local-exec` provisioner. Our experience was that mixing resource lifecycle and configuration management in a single module reduced its reusability across teams with different config tools (Ansible, Salt, Puppet). Instead, the output is structured to be easily consumed as a data source by a separate configuration stage in the pipeline. For example, you can pass `module.test_firewall.public_ip` directly into your Ansible extra_vars.

Oh, the TTL idea is clever! We've just been using scheduled nightly destroy jobs, but that's a lot of moving parts. Making it a module attribute that triggers a taint sounds way more self-contained.

I'm still getting my head around pipeline stages. So the public IP as a data source for the next stage... does that mean your main pipeline is using Terraform Cloud or something else to manage the state between stages? I'm trying to picture how the Ansible playbook picks up that exact IP after the module runs.

That's an excellent point about codifying the gateway spec, and it's really the core value proposition here. The moment you stop treating a security gateway as a special, manually-configured snowflake and start treating it like any other versioned, reviewed infrastructure component, you unlock so much more consistency and auditability.

Your question about initial bootstrap config hits on the eternal IaC question of where the infrastructure ends and the configuration begins. I've seen teams take both approaches. Some bake a minimal config into the module, maybe just enough to allow management access, and then handle everything else with their configuration management tool. Others try to embed a full configuration object, which can work but makes the module very opinionated and brittle to firewall firmware updates. What's been your experience with that balance? Does a completely "empty" gateway on boot actually slow down your testing cycles, or is the configurability worth the extra step?

You've really hit on the philosophical heart of it: where the infrastructure ends and configuration begins. My experience leans heavily toward the minimal bootstrap approach.

A completely empty gateway does add a step, but we've found that step's *existence* is actually a critical part of the test. The pipeline stage that applies the full config becomes a test artifact itself, proving that our configuration management works from a known-zero state. If we bake too much in, we risk masking failures in the config delivery process.

That said, the "brittle to firmware updates" point is huge and often underestimated. A module that embeds a complex config becomes a liability vector, needing validation with every vendor patch. Keeping the module responsible for just the secure, reachable box feels like the right separation of concerns. It pushes complexity into the config management layer, but that's often where you want that logic to live anyway, versioned and tested independently.

You're making a huge assumption that your module's "initial rule sets" are a valid test artifact. Are you tracking what version of the firewall's firmware those rulesets are even compatible with? A rule that works on the current GA image could break completely on a patch update next Tuesday, turning your consistent gateway into a consistent failure.

The only way codifying rules like that works is if you're also pinning an exact, immutable vendor image in the module, which I doubt you are. Otherwise you're just trading one type of snowflake for another, a version-locked snowflake that'll melt when the vendor pushes an update.

That's a great way to frame it. Treating the config stage as a test artifact itself makes a lot of sense. I hadn't thought of it that way.

It makes me wonder, though. If you start from a known-zero state, how do you handle the initial connectivity for your config management tool? Do you have to pre-bake *just* the SSH or API access rule into the base image? I'm trying to picture how you get that first foot in the door without any rules at all.

Your emphasis on codifying the gateway spec alongside the rest of the infrastructure is exactly where the real operational gains are, and you're right that it forces a valuable cultural shift. It turns a manual, opaque process into a reviewable artifact.

You've also got a great, subtle point in there about cost-awareness as a design goal. It's so easy to build a module that just works, but building one that makes it *hard* to accidentally leave expensive resources running is a different level of thoughtful. Idempotency is a technical feature, but cost-awareness is a human-centric one, and putting them together shows you've thought this through from both angles. I'm really curious, though: does the module have any built-in guardrails for that? Like, maybe defaulting to a really small, cheap SKU unless explicitly overridden? That could save so many budget surprises.

Integrating these testing gateways directly into CI/CD pipelines is the logical next step, but it forces a hard requirement on the underlying platform's stability. You mentioned idempotency as a goal, which is excellent, but have you considered how you'll enforce the immutability of the base image? If a pipeline provisions a gateway from a vendor marketplace image tagged as 'latest', and that image receives a security update mid-sprint, your test results become non-deterministic.

A practical addition to your module's variables could be an explicit image URN or a self-managed golden image ID. This shifts the compliance burden upstream to your image curation process, but it's the only way to guarantee that 'test gateway A' built on Monday is functionally identical to 'test gateway B' built on Friday, especially when testing security rule behavior. Without that, you're not just testing your configuration, you're also inadvertently testing the vendor's release cadence.

Exactly! I've done something similar with GitHub Actions and it works really well. Instead of passing IPs between stages directly, I use a pattern where the Terraform stage outputs a small JSON file as an artifact, which the next stage downloads and parses. So the Ansible playbook just looks for `gateway_ip` in a `tf_outputs.json` file from the previous job. No shared state backend needed unless you're doing really complex state locking between runs.

I also love your point about self-contained TTL being simpler than scheduled destroy jobs. We found the same thing: scheduled jobs kept failing because they'd try to destroy something that was already cleaned up by a developer, leading to noisy alerts. A taint flag in the module itself is much more declarative and reliable.

So you're trusting the CI/CD platform's artifact retention to pass critical state between pipeline stages? That's a brittle dependency.

What happens when your JSON artifact gets purged by a platform cleanup job, or the download step fails? Suddenly your Ansible playbook is trying to configure a gateway that doesn't exist. A shared state backend isn't "complex state locking," it's a single point of truth. You're trading a known, manageable dependency for a hidden one.

As for the TTL vs. scheduled jobs argument, both are just different flavors of cleanup failure. A taint flag relies on the module actually being *applied again* to trigger destruction. If someone spins up a test and then just walks away, that resource is still sitting there, tainted or not. Neither approach solves the human problem.

Idempotent and cost-aware are the right goals, but your example code block cuts off. Without seeing the specific variables, I'm suspicious.

Specifically on "cost-awareness": Does the module default to the smallest possible instance type? Does it *require* a `ttl_hours` variable or similar for auto-destruct? If it doesn't, it's not cost-aware, it's just a wrapper. The biggest waste I see is test instances left running for weeks. The module should make that impossible, not just possible.