Stategraph: Terraform state as a distributed systems problem

Hmm

I don’t see the state file as a complete downside. It is very simple and very easy to understand. It makes it easy to tell or predict what terraform will do given the current state and desired state.

Its simpleness makes troubleshooting easier: the state files are easy to read and manipulate or repair in the event of a drift, mismatch, or botched provider update.

With the solution proposed it feels like the state becomes a black box I shouldn’t put my hands in. I wonder how the troubleshooting scenarios change with it.

Personally, I haven’t ran into the scaling issue described; at any given time there is usually only one entity working with the state file. We do use terragrunt for larger systems but it is manageable. ~1000 engineer org.

I can't help but wonder whether the problem being addressed is the result of two antipatterns.

The first is that the scope being managed by a single Terraform application is too broad (e.g., thousands of resources instead of tens or hundreds). File-level locking is fine for small databases with few to no concurrent writers, but as more users come in, and the database gets bigger, you need record-level locking. For Terraform state files, it begs the question why the database got so big and why there were so many concurrent users in the first place.

Second, Terraform state files are a cache but they're being mistreated as a source of truth. This isn't the user's fault but it is the result of (understandable) impatience which results in inevitable shortcut-seeking. It's been a risk since Terraform's inception, and it won't go away as long as people complain that collecting current actual state from the resource provider is too slow.

I'm wondering how access controls play into this.

Team A manages VPCs and Security groups, for example.

Team B manages autoscaling groups, EC2, etc.

It's great that now the two teams can look after their own things and not be too worried about resource contention with the other team. But if it's a centralized Postgres database (as you seem to be suggesting?) and both teams have write access to it...

How do we prevent teams from making changes to stuff that isn't "theirs" ?

And if the answer is "well this team only has IAM access to resources xyz", well then might it be a little tricky to represent the Stategraph DAG permission boundaries in IAM policy?

(ps: huge fan of terrateam's offerings -- Alex from tfstate.com)

Having done some work with building graph representation of compute resources (by importing tfstate & syncing from aws) and its a very useful representation for building things like visualizations and detecting dependencies. Moving tfstate to a real distributed graph system would help solve a LOT of the nasty hacks they mention in this article that I have run into HARD when working with very large numbers of resources and multiple teams/team sizes.

Hey! One of the Stategraph developers here and can answer any questions. The major motivation is just how small scale Terraform/Tofu start to breakdown and creates work for users when they have to refactor for performance issues that shouldn't exist. So we want a drop in solution that just dissolves those issues without the user having to do anything.

Very interesting. I found myself nodding YES the whole way through the post. Something like this could lead to a large shift in how we manage infrastructure. We split terraform configs for more reasons than just splitting state of course, but something like this could make other approaches to organizing things more viable. Really cool and will be keeping an eye on this.

> The Terraform ecosystem has spent a decade working around a fundamental architectural mismatch: we're using filesystem semantics to solve a distributed systems problem. The result is predictable and painful.

You portray this as a design flaw, but it's just the Hashicorp marketing funnel towards hosted Terraform, which solves the arbitration problems that you encounter at scale while allowing Hashicorp to give the cli tooling away for free.

It's an interesting proposal because they correctly call out that segmenting state files by workspace/environment in a very judicious way causes its own issues as you approach scale or have to work across environments. There is an entire industry of tools and services that help to streamline this process for you, but it still feels very hacky.

I'm curious if this will be compatible with tools like Spacelift or Env Zero, or if they are going to build their own runner/agent to compete in that space.

I don't think a DAG makes sense as a model here. I've always likened terraform apply to setting what would be called a "waypoint" in robotics, or a "keyframe" in animation. The system doesn't immediately change state to the new state all at once, but it starts to tend towards the new desired state.

While the intermediary states might form a graph when considering different subsystems, the desire to move towards a given state should probably appear serial over time. When you make a terraform transaction, you have to coordinate in a serializable way with everyone else managing the desired state, even though the actual state will be messy along the way.

This looks awesome but what is the end state (pun intended) going to be? Will this be an open source project? Commercial closed-source? Somewhere in between?

This is very cool. I love the idea of querying the state, and it opens up a ton of very easy reporting options.

This is cool and useful for teams with huge states and slow locks. Terraform, while great, still has lots of room for improvement.

I keep wondering though if split state files isn’t a good thing in some sense anyway. It isolates a lot of problems. Access, obviously. Another common theme is that applying tends to be a game of roulette, even if you haven’t changed anything. Cloud vendor added or renamed something in their backed. Provider update made some field deprecated. Expected state drift that wasn’t properly marked as ”ignore_changes”. Unexpected state drift by your over-excited intern. When I as an app-developer apply a simple config file change, I really don’t want to be bothered about dirty state in the networking backbone that I understand nothing about.

It’s also not entirely clear how the solution keeps track of the desired state if multiple actors are changing it at the same time. Wouldn’t one successful apply make the next person, who don’t have your local changes, revert it back on first apply? Does this expect heavy use of resource targeting?

Very cool. Biggest question I have is how users with large setups where Terraform state has already been split would migrate to this. Would existing state blobs be namespaced into the One True State Graph in PG? Would Stategraph know how to merge different state blobs that are pointing to the same real-life resources? Will Stategraph promote some kind of convention for how state should be named, so that new projects can on-board to using the same state? Should Terraform fit a monorepo or polyrepo model with this kind of backend?

How does this compare with Pulumi? AFAIK they also don't have a state file and relay on an external database to store state. Is your locking granularity better?

As someone who worked on projects which "solved" this issue by basically having one stack in one repo by resource sub-set (an ALB fronting an ASG will result in one repo for the ALB and one repo for the ASG), I can only welcome any solution trying to simplify team collaboration on Terraform stacks!

This is awesome. Having a single state for all resources in an environment is critical for keeping all the moving pieces in check and a core design aspect of Kubestack. But the growing state files quickly become a bottleneck. I'm definitely giving this a good test drive. Very excited.

Not an expert, but doesn't microservices help with this. Each microservice has its own YAMLesque resource descriptor (TF, cloudformation, whatever) and is managed independently. My team can add a SQS or S3 without locking your team.

I might be wrong regarding more sophisticated infra though.

Are there any statistics/analyses for the popularity of these different configuration management languages/frameworks (Terraform, Pullumi etc) in cloud settings? Trying to figure out which one(s) are worth learning.

If you use a tool like Atmos (https://atmos.tools/) you kind of fix this issue already for free - because it takes the place of the root module, it actually manages the state of each sub module separately (they each have their own individual state file rather than being converged into one).

If you're at the point of managing thousands of resources inside a single statefile, and that makes the most sense to your setup: you've outgrown terraform.

can it be a sqlite db in s3 with locking implemented with s3?

This is the least of the problems. The big problem is the shared cache. Supposedly OpenTofu fixed it but Terraform proper is still not allowing multiple Terraform plans and/or applies in parallel over the same cache. Atlantis claimed that it fixed it, but it didn't. So pathetic!

so kind of like crossplane where each resource is managed individually?

I deeply believe that the whole "state" approach with TF is flawed. You end up doing a 3-way merge between the actual state, the desired state, and the recorded state every time you try to make changes.

Long time ago, I was simply doing stuff like this:

> resources = describe_resources_by_tag(env_name=env, some_tag=tag) > if resource_doesnt_exist(resources, some_resource): > create_resource(resource)

This was very robust and easy to explain. You look around the system, using some tag-based filtering (in AWS, GCP, Azure) and then perform actions to bring the system to the desired state.

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