0x74696d
Joined 11 years ago
Joined 11 years ago
Yeah, I saw the recent post about reducing rqlite disk space usage. Using the on-disk sqlite as both the FSM and the Raft snapshot makes a lot of sense here. I'm curious whether you've had concerns about write amplification though? Because we have only the periodic Raft snapshots and the FSM is in-memory, during high write volumes we're only really hammering disk with the Raft logs.
> Do you find it in the field much with Nomad? I've managed to introduce new Raft Entry types very infrequently during rqlite's 10-years of development, only once did someone hit it in the field with rqlite.
My understanding is that rqlite Raft entries are mostly SQL statements (is that right?). Where Nomad is somewhat different (and probably closer to the OP) is that the Raft entries are application-level entries. For entries that are commands like "stop this job"[0] upgrades are simple.
The tricky entries are where the entry is "upsert this large deeply-nested object that I've serialized", like the Job or Node (where the workloads run). The typical bug here is you've added a field way down in the guts of one of these objects that's a pointer to a new struct. When old versions deserialize the message they ignore the new field and that's easy to reason about. But if the leader is still on an old version and the new code deserializes the old object (or your new code is just reading in the Raft snapshot on startup), you need to make sure you're not missing any nil pointer checks. Without sum types enforced at compile time (i.e. Option/Maybe), we have to catch all these via code review and a lot of tedious upgrade testing.
> it requires discipline on the part of the end-users too.
Oh for sure. Nomad runs into some commercial realities here around how much discipline we can demand from end-users. =)
[0] https://github.com/hashicorp/nomad/blob/v1.8.2/nomad/fsm.go#... [1] https://github.com/hashicorp/nomad/blob/v1.8.2/nomad/fsm.go#...
The in-memory state can be whatever you want, which means you can build up your own application-specific indexing and querying functions. You could just use sqlite with :memory: for the Raft FSM, but if you can build/find an in-memory transaction store (we use our own go-memdb), then reading from the state is just function calls. Protecting yourself from stale reads or write skew is trivial; every object you write has a Raft index so you can write APIs like "query a follower for object foo and wait till it's at least at index 123". It sweeps away a lot of "magic" that normally you'd shove into a RDBMS or other external store.
That being said, I'd be hesitant to pick this kind of architecture for a new startup outside of the "infrastructure" space... you are effectively building your own database here though. You need to pick (or write) good primitives for things like your inter-node RPC, on-disk persistence, in-memory transactional state store, etc. Upgrades are especially challenging, because the new code can try to write entities to the Raft log that nodes still on the previous version don't understand (or worse, misunderstand because the way they're handled has changed!). There's no free lunch.
But it's not clear to me from a casual glance at the the docs whether Distelli lives inside the container during those hooks? That's part of the distinction of the Autopilot Pattern is making the higher-level orchestration layer as thin as possible.
(As far as the root, some of it is derived from my experiences as a perhaps-foolishly-early adopter of Docker in prod at my previous gig at a streaming media startup. The rest is derived from both principals with which Joyent's own Triton infra is built and our experiences speaking with enterprise devs and ops teams.)
I think this is the most important problem IOPipe is trying to solve. Portability between platforms is a good goal but achievable with some discipline about avoiding the proprietary bits of the platform. Making "serverless" software operable to the same (or better) degree than traditional software deployment is the key.
Meh. I get your sentiment here, but I build and deploy on Linux and I post about the stuff I work on. I don't post about the Windows stuff that I haven't worked on in years. And I assume a level of intelligence in my readers that they can translate whatever might be generally applicable into their own platform in the same sense that I don't grumble about Raymond Chen's `Old New Thing` not being directly applicable to my own work but still enjoy it.
You've summed up the entire reasoning behind my post more succinctly than I could. Thanks.
The core of my work is on the operations side rather than on development (although I do a good bit of that as well), so my perspective is that this initial overhead is a one-time cost for using a library, and that I can live with that.
> I think it's time go devs acknowledge the fact that there is an serious issue here, instead of resorting to the ususal "you don't need that in go".
Encountering this and a lot of "well this is the way Google does is so we should too" was a big part of what inspired this post.
That being said, when Kinesis previewed it had only Java bindings for KCL. Not sure if that's still the case, but that'd be a limiting factor for our shop unfortunately.