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Etcd – The Road to 1.0

coreos.com

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Re: Etcd – The Road to 1.0

#11

Post by darklajid »

bashcoder wrote: post #7

I know that there are lots of heavyweight folks who swear by Zookeeper as both a reliable and powerful tool, and for good reason. Unfortunately the docs can be fairly inscrutable, even for experts, and it typically requires the maintenance of a separate cluster of Zookeeper nodes. So I like that etcd is a fundamental component of CoreOS, with these features: 1. Written from scratch in Go 2. Implements the Raft protoc…

No offense, I just don't get it: Why is 1) a feature for you? Everything else on the list kinda makes sense (I understand that this describes something I'd call a feature), but 'written from scratch' or 'in Go'?

Can you explain what excites you about that?

Re: Etcd – The Road to 1.0

#12

Post by ecnahc515 »

darklajid wrote: post #11
bashcoder wrote: post #7

I know that there are lots of heavyweight folks who swear by Zookeeper as both a reliable and powerful tool, and for good reason. Unfortunately the docs can be fairly inscrutable, even for experts, and it typically requires the maintenance of a separate cluster of Zookeeper nodes. So I like that etcd is a fundamental component of CoreOS, with these features: 1. Written from scratch in Go 2. Implements the Raft protoc…

No offense, I just don't get it: Why is 1) a feature for you? Everything else on the list kinda makes sense (I understand that this describes something I'd call a feature), but 'written from scratch' or 'in Go'? Can you explain what excites you about that?

Probably the fact that you get a single binary (unlike interpreted languages), and that it isn't a mix of Go and C meaning I worries about c libraries.

Re: Etcd – The Road to 1.0

#13

Post by babo »

ecnahc515 wrote: post #12
darklajid wrote: post #11

Earlier quoted context omitted.

No offense, I just don't get it: Why is 1) a feature for you? Everything else on the list kinda makes sense (I understand that this describes something I'd call a feature), but 'written from scratch' or 'in Go'? Can you explain what excites you about that?

Probably the fact that you get a single binary (unlike interpreted languages), and that it isn't a mix of Go and C meaning I worries about c libraries.

Just to note, zookeeper is written in Java.

Re: Etcd – The Road to 1.0

#14

Post by stormbrew »

robszumski wrote: post #9
stormbrew wrote: post #8

Earlier quoted context omitted.

> 4. Runs on every node in a cluster Is that so? When looking at it I distinctly remember it advising running a set of 3-9 nodes of etcd (not necessarily separate from other things).

The functionality to handle this is mentioned in the blog post: "standby" peer mode. "Our upcoming release, etcd 0.4, adds a new feature, standby mode. It is an important first step in allowing etcd clusters to grow beyond just the peers that participate in consensus."

Fair enough, it just sounded like the GP was describing something inherent rather than something new, and it didn't mesh with my understanding of how etcd worked to date.

Re: Etcd – The Road to 1.0

#16

Post by bashcoder »

darklajid wrote: post #11
bashcoder wrote: post #7

I know that there are lots of heavyweight folks who swear by Zookeeper as both a reliable and powerful tool, and for good reason. Unfortunately the docs can be fairly inscrutable, even for experts, and it typically requires the maintenance of a separate cluster of Zookeeper nodes. So I like that etcd is a fundamental component of CoreOS, with these features: 1. Written from scratch in Go 2. Implements the Raft protoc…

No offense, I just don't get it: Why is 1) a feature for you? Everything else on the list kinda makes sense (I understand that this describes something I'd call a feature), but 'written from scratch' or 'in Go'? Can you explain what excites you about that?

I listed what I like. "Excites" is your word.

I guess what I meant by "from scratch" is that they aren't burdened by legacy code, and aren't limited to using the Paxos algorithm.

If you look at Deis, for example, it basically outsources a lot of node management to Chef Server, which in my view creates a great deal of technical debt on day one.

Re: Etcd – The Road to 1.0

#17

Post by bashcoder »

fizx wrote: post #10
stormbrew wrote: post #8

Earlier quoted context omitted.

> 4. Runs on every node in a cluster Is that so? When looking at it I distinctly remember it advising running a set of 3-9 nodes of etcd (not necessarily separate from other things).

I don't know that that's necessarily a good idea. As you (perhaps automatically) expand and collapse the cluster, you'll need to make sure to communicate to all nodes what the new cluster size is. If some nodes don't know the correct quorum count, split-brain! Also, coordination services are typically critical, so its important to isolate from to the bugs in the adhoc code you're writing for your web tier, a crazy qu…

I probably should have said that it "can" run on any node. Yes, currently it does run on every node, but their roadmap doesn't have the requirement that every node be actively participating in elections.

I'm sure that you have seen fleets of dedicated Zookeeper nodes. I rather like that etcd is simply a service that can run on any node, and does not require a separate role-specific fleet of servers just to do coordination. That was the point I was attempting to make.

Re: Etcd – The Road to 1.0

#18

Post by ekimekim »

bashcoder wrote: post #7

I know that there are lots of heavyweight folks who swear by Zookeeper as both a reliable and powerful tool, and for good reason. Unfortunately the docs can be fairly inscrutable, even for experts, and it typically requires the maintenance of a separate cluster of Zookeeper nodes. So I like that etcd is a fundamental component of CoreOS, with these features: 1. Written from scratch in Go 2. Implements the Raft protoc…

Personally, my preference for zookeeper comes from the API. To me, the ZK API and docs were far more understandable than the etcd ones. The etcd api docs appear to be a collection of examples, not reference docs. It does a poor job of explaining the possible operations and what various options will do, particularly in what combinations of options are allowed.

In fact, I had to resort to running test queries against a running etcd server just to work out the proper semantics of some of the arguments.

Re: Etcd – The Road to 1.0

#19

Post by peterwwillis »

argc wrote: post #2

Is there any benefit to using coreOS when you don't need a million machines? How much work is it to start with, for example, if you have no idea what your scaling needs will be in the future?

The only significant benefit over traditional operating systems/network services is it's designed to work on flaky hardware and networks. The only use cases i've found for decentralized distributed networks of application services (other than obscure stuff like parallel processing of large datasets) is when you have no guarantees of availability. As far as "scaling", you don't need coreOS to build a scalable network (and i've seen no performance benchmarks of coreOS running on thousands of machines at a time, so I have no idea how well it scales)

Re: Etcd – The Road to 1.0

#20

Post by mavelikara »

bashcoder wrote: post #16
darklajid wrote: post #11

Earlier quoted context omitted.

No offense, I just don't get it: Why is 1) a feature for you? Everything else on the list kinda makes sense (I understand that this describes something I'd call a feature), but 'written from scratch' or 'in Go'? Can you explain what excites you about that?

I listed what I like. "Excites" is your word. I guess what I meant by "from scratch" is that they aren't burdened by legacy code, and aren't limited to using the Paxos algorithm. If you look at Deis, for example, it basically outsources a lot of node management to Chef Server, which in my view creates a great deal of technical debt on day one.

> and aren't limited to using the Paxos algorithm

ZK uses the ZAB protocol, which is similar but not the same as Paxos.

https://cwiki.apache.org/confluence/display/ZOOKEEPER/Zab+vs...

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