6 ms·

Etcd 0.3.0 – Improved Cluster Discovery, API Enhancements and Windows Support

50 points by polvi 13y ago

aabalkan 13y ago
Especially Windows support is cool news. I am following etcd project, it's serious and can change server configuration world. Thanks Alex!
cenkalti 13y ago
Congratz guys, this is a big improvement from 0.2.0. Keep up good work!
Touche 13y ago
I can't figure out what etcd is. Any help?
- staunch 13y ago
  "A highly-available key value store for shared configuration and service discovery. etcd is inspired by zookeeper and doozer..." -- https://github.com/coreos/etcd https://github.com/coreos/etcd
  - ballard 13y ago
    Except that it's not. Zookeeper was a major pain to get where it is.
    - deleted 13y ago
      [deleted]
- jarito 13y ago
  It is a distributed configuration management clustering product like zookeeper. It simplifies the creation and sharing of mostly configuration data in clustered or distributed systems.
  - ballard 13y ago
    It's trying to solve with marketing what Chef does. There is more to configuration management that templating files, but in inspection and having other services arriving at other states.
    - vidarh 13y ago
      It is not even trying to solve remotely the same issues as Chef. For starters, it is not going to install or uninstall packages or modify files, or nearly any of the things that a typical Chef recipe might do.
  - Touche 13y ago
    I don't know what that means or what zookeeper is... Can you explain the problem it solves?
    - sethhochberg 13y ago
      Imagine you're working with a processing system made up of tens or hundreds of computers all (usually) identically configured, networked together and solving small chunks of a large problem. This is software to minimize the effort required to configure all of those individual systems which make up the "compute cluster".
    - vidarh 13y ago
      Your web app needs to know what IP address, username and password to connect to the database on. If it's all one the same box, that's trivial. But imagine you have several app serves, and several other systems that all needs to talk to the database. Then one day you need to change details of the database server. Now you can either use a tool to update all the configurations (or do it by hand), or you can have all of these apps pull the database config from a distributed directory of some sort. Etcd is such a directory. Similar to LDAP, but simpler (LDAP requires you to write schemas, and decide which attributes to index on and in set up replication hierarchies). Some people also use DNS for this (you can put arbitrary data in a private DNS server).
    - 13y ago
- DannoHung 13y ago
  Y'know how you can use ENV on Linux to have programs be configured or tell multiple programs what port something is listening on? Imagine that, but across multiple servers at once. Plus a few other things that some use cases have been built up for.
- insaneirish 13y ago
  It can mean different things to different people. I will try to explain how I came to understand how etcd could be valuable for me, which may not be indicative of anyone else's use. We have lots of configuration automation tools: Chef, Puppet, Ansible, SaltStack, etc. These tools make it easier to orchestrate the modification of configuration files on a node. That is well and good. However, what is my "source of truth" for how things should be configured? Does the fact that node593958.my.co is my primary database server for app foo belong inside Chef, or another tool, or is it more suited for a "directory" of sorts? No one can answer that but you. But, if you decide that it shouldn't be embedded in your configuration orchestration tool, you may decide to put it in a key value store like etcd. etcd could expose (via REST), something like: .../apps/foo/primary_db = node593958.my.co Configuration management could then key off of that source of truth to configure the application appropriately. etcd exposes an easy to use REST interface to arbitrary storage of hierarchical keys and values. Nothing is new under the sun. During the first five minutes I was playing around with etcd, I realized I was effectively reinventing LDAP. This is neither wrong nor right, it's simply a different tool for the job. If you like REST and simple interfaces, it's probably a good tool.
bkirwi 13y ago
I'm curious to know more about the garbage collection of stale peers. - AFAIK, etcd is built on RAFT, which relies on a 'joint majority' method of transitioning cluster membership. Are there any issues forming agreement on what the new membership should be when it's unclear what nodes are still supposed to be part of the cluster? - In the land of ZooKeeper, cluster configurations are typically very very stable, so tracking membership takes very little information. Is etcd targeted to more dynamic environments where the garbage generated by entering and leaving nodes is significant?
- philips 13y ago
  etcd isn't designed for significantly dynamic environments but we certainly want to make it easy for people to add and remove machines at runtime. We have basic support for runtime cluster configuration but are building out a more complete API. The current proposal that is being built can be found over here: http://thread.gmane.org/gmane.comp.distributed.etcd/168 http://thread.gmane.org/gmane.comp.distributed.etcd/168 As you point out there is no magic garbage collection of stale peers. You have to explicitly delete nodes that you don't expect to be participating any longer.
nl 13y ago
Discovery looks interesting. Can it be used for a client to discover a cluster? I've been digging into Docker link containers a bit. I'm not entirely comfortable with how they work,and I'm not really sure why. The only thing I can put my finger on is that I feel like discovery is a separate concern to deployment. But at the same time they are so closely linked o can understand why Docker needs to tackle it. Is there a way etcd can work better with Docker links? Maybe it could automatically read/write Docker published ENV variables or something? Though I don't think that will quite work across physical machines without some additional work.
- philips 13y ago
  > Discovery looks interesting. Can it be used for a client to discover a cluster? It certainly could be extended for that. We haven't done anything with discovery to help with that process yet though. > Is there a way etcd can work better with Docker links? There is a lot of room to explore here. Including: - Automatically registering exposed ports from running containers into etcd for service discovery. - Using information in etcd to manage a smart proxy that would proxy requests. This would be the "Link via an Ambassador" but etcd would help coordinate. Both of these would be good things to build and see how they work and feel in practice. There are also some interesting alternatives to doing the links thing such as using some network namespace tricks to avoid passing metadata around via environment variables and simply expose services directly into a container: https://coreos.com/blog/Jumpers-and-the-software-defined-localhost/ https://coreos.com/blog/Jumpers-and-the-software-defined-loc...
  - nl 13y ago
    > Discovery looks interesting. Can it be used for a client to discover a cluster? >> It certainly could be extended for that. We haven't done anything with discovery to help with that process yet though. So what is the current best practice for etcd discovery? Environment variable? mDNS might be nice, too (Though I guess mDNS is kinda, almost an alternative for a subset of what etcd does). http://blogs.gnome.org/danni/2014/02/02/a-libnss-plugin-for-docker/ http://blogs.gnome.org/danni/2014/02/02/a-libnss-plugin-for-... looks interesting too. I read the Jumper post thing when it was HN. I need to think about that some more.
ballard 13y ago
This is a pure marketing story pushing a bad solution. Hiera, a simple hierarchal property distribution system using a backend of Zookeeper plus puppet or chef is far superior. Etcd is the PHP of configuration management.
- danieldk 13y ago
  Wow. I know neither etcd or Hiera. But please provide some arguments against etcd if you think it is bad, rather than just bashing it. It would be interesting to know the cons and pros of both solutions.
  - ballard 13y ago
    I'm bashing it because it oversimplifies the problem and claims to be a solution that doesn't address the irreducibility of the problem. It's great for a host file but scp can do that. It doesn't coordinate the transition of services to other states. Puppet does an incredible amount of work (dependency satisfaction) to get things where you want them to be. Configuration management is as much management order of operations as well as what files should contain what. There's not much separating the two because you have to usually change them between states. Chef does this to, but in a simpler way. Cfengine was a past attempt, but is really complicated double work of what runs on a server and what runs on a managed node.
    - rdtsc 13y ago
      > It doesn't coordinate the transition of services to other states. Can you be more specific? So to co-ordinate transitions what else would it need -- multi-key transactions? Surely you have good reason to jump in and criticize it so sharply...
      - ballard 13y ago
        Configuration management transactions. Puppet has the notion of stages. Yes because it's marketing an unproven technology as a solution when better things already exist. Someone I know from (OpsCode||Puppet) even further the recommendation of zk as basically the only proven consistent KVS. A better approach should be to do what other cloud shops have done and ship ZK appliances. Pushing new tech on customers is using them to beta test unproven tech, which is reinventing the wheel and risky.
vidarh 13y ago
The discovery mechanism looks clumsy to me. There's no way we'd rely on a public discovery service, for example. If we're going to hardcode configuration information - such as the URL of a discovery service that may or may not be up or reachable, we might as well hardcode the addresses of a few peers. And running a second etcd cluster to bring up the main one seems pointless. Either it's turtles all the way down, or you then need to hardcode config information for the second cluster, in which case it serves little purpose. I'd rather have a mechanism where each peer takes a list of possible peers and tries to connect, with a method for deciding when there is quorum to elect an initial leader and start allowing writes (that's easy enough by introducing a config option to decide if a peer is "blessed" to be part of the initial leadership election, and how many blessed peers must be connected to have quorum - just needs to be enough to form a majority of blessed peers to prevent more than one subset from electing a leader before they manage to connect) Am I missing something?
- nl 13y ago
  Quoting the post: In previous releases, a human had to pick a leader, pass a list of -peers to all of the followers and maintain that list going forward. Presumably that method is still there?
  - robszumski 13y ago
    Yep, you can still hardcode a list of peers via flag or config file. I think you can even use both a peer list and a discovery token at the same time.
- ballard 13y ago
  This is why top-down, single-source of truth is mostly the best way for core infrastructure. No pun intended. It's important for some parts to not be infinitely reconfigurable or dynamic because it would create chaos and service dependency deadlock/DoS. Most people not running bare metal don't know the lessons of how and why things underneath are they way they are and the sensible limits what's possible. It's also more secure because if it's possible to dictate all of the service details, it's much easier to run a lean and locked-down infrastructure. CoreOS by itself looks great. More JEOS distros need to happen. Trying to bundle more unproven things just looks marketing led the product.
baghali 13y ago
Has anyone checked out serf http://www.serfdom.io/ http://www.serfdom.io/ if yes what are the pros and cons of etcd and serf?

50 points by polvi 13y ago

Especially Windows support is cool news. I am following etcd project, it's serious and can change server configuration world. Thanks Alex!

cenkalti 13y ago

Congratz guys, this is a big improvement from 0.2.0. Keep up good work!

Touche 13y ago

I can't figure out what etcd is. Any help?

staunch 13y ago
"A highly-available key value store for shared configuration and service discovery. etcd is inspired by zookeeper and doozer..." -- https://github.com/coreos/etcd https://github.com/coreos/etcd
- ballard 13y ago
  Except that it's not. Zookeeper was a major pain to get where it is.
  - deleted 13y ago
    [deleted]
jarito 13y ago
It is a distributed configuration management clustering product like zookeeper. It simplifies the creation and sharing of mostly configuration data in clustered or distributed systems.
- ballard 13y ago
  It's trying to solve with marketing what Chef does. There is more to configuration management that templating files, but in inspection and having other services arriving at other states.
  - vidarh 13y ago
    It is not even trying to solve remotely the same issues as Chef. For starters, it is not going to install or uninstall packages or modify files, or nearly any of the things that a typical Chef recipe might do.
- Touche 13y ago
  I don't know what that means or what zookeeper is... Can you explain the problem it solves?
  - sethhochberg 13y ago
    Imagine you're working with a processing system made up of tens or hundreds of computers all (usually) identically configured, networked together and solving small chunks of a large problem. This is software to minimize the effort required to configure all of those individual systems which make up the "compute cluster".
  - vidarh 13y ago
    Your web app needs to know what IP address, username and password to connect to the database on. If it's all one the same box, that's trivial. But imagine you have several app serves, and several other systems that all needs to talk to the database. Then one day you need to change details of the database server. Now you can either use a tool to update all the configurations (or do it by hand), or you can have all of these apps pull the database config from a distributed directory of some sort. Etcd is such a directory. Similar to LDAP, but simpler (LDAP requires you to write schemas, and decide which attributes to index on and in set up replication hierarchies). Some people also use DNS for this (you can put arbitrary data in a private DNS server).
  - 13y ago
DannoHung 13y ago
Y'know how you can use ENV on Linux to have programs be configured or tell multiple programs what port something is listening on? Imagine that, but across multiple servers at once. Plus a few other things that some use cases have been built up for.
insaneirish 13y ago
It can mean different things to different people. I will try to explain how I came to understand how etcd could be valuable for me, which may not be indicative of anyone else's use. We have lots of configuration automation tools: Chef, Puppet, Ansible, SaltStack, etc. These tools make it easier to orchestrate the modification of configuration files on a node. That is well and good. However, what is my "source of truth" for how things should be configured? Does the fact that node593958.my.co is my primary database server for app foo belong inside Chef, or another tool, or is it more suited for a "directory" of sorts? No one can answer that but you. But, if you decide that it shouldn't be embedded in your configuration orchestration tool, you may decide to put it in a key value store like etcd. etcd could expose (via REST), something like: .../apps/foo/primary_db = node593958.my.co Configuration management could then key off of that source of truth to configure the application appropriately. etcd exposes an easy to use REST interface to arbitrary storage of hierarchical keys and values. Nothing is new under the sun. During the first five minutes I was playing around with etcd, I realized I was effectively reinventing LDAP. This is neither wrong nor right, it's simply a different tool for the job. If you like REST and simple interfaces, it's probably a good tool.

bkirwi 13y ago

I'm curious to know more about the garbage collection of stale peers. - AFAIK, etcd is built on RAFT, which relies on a 'joint majority' method of transitioning cluster membership. Are there any issues forming agreement on what the new membership should be when it's unclear what nodes are still supposed to be part of the cluster? - In the land of ZooKeeper, cluster configurations are typically very very stable, so tracking membership takes very little information. Is etcd targeted to more dynamic environments where the garbage generated by entering and leaving nodes is significant?

philips 13y ago
etcd isn't designed for significantly dynamic environments but we certainly want to make it easy for people to add and remove machines at runtime. We have basic support for runtime cluster configuration but are building out a more complete API. The current proposal that is being built can be found over here: http://thread.gmane.org/gmane.comp.distributed.etcd/168 http://thread.gmane.org/gmane.comp.distributed.etcd/168 As you point out there is no magic garbage collection of stale peers. You have to explicitly delete nodes that you don't expect to be participating any longer.

nl 13y ago

Discovery looks interesting. Can it be used for a client to discover a cluster? I've been digging into Docker link containers a bit. I'm not entirely comfortable with how they work,and I'm not really sure why. The only thing I can put my finger on is that I feel like discovery is a separate concern to deployment. But at the same time they are so closely linked o can understand why Docker needs to tackle it. Is there a way etcd can work better with Docker links? Maybe it could automatically read/write Docker published ENV variables or something? Though I don't think that will quite work across physical machines without some additional work.

philips 13y ago
> Discovery looks interesting. Can it be used for a client to discover a cluster? It certainly could be extended for that. We haven't done anything with discovery to help with that process yet though. > Is there a way etcd can work better with Docker links? There is a lot of room to explore here. Including: - Automatically registering exposed ports from running containers into etcd for service discovery. - Using information in etcd to manage a smart proxy that would proxy requests. This would be the "Link via an Ambassador" but etcd would help coordinate. Both of these would be good things to build and see how they work and feel in practice. There are also some interesting alternatives to doing the links thing such as using some network namespace tricks to avoid passing metadata around via environment variables and simply expose services directly into a container: https://coreos.com/blog/Jumpers-and-the-software-defined-localhost/ https://coreos.com/blog/Jumpers-and-the-software-defined-loc...
- nl 13y ago
  > Discovery looks interesting. Can it be used for a client to discover a cluster? >> It certainly could be extended for that. We haven't done anything with discovery to help with that process yet though. So what is the current best practice for etcd discovery? Environment variable? mDNS might be nice, too (Though I guess mDNS is kinda, almost an alternative for a subset of what etcd does). http://blogs.gnome.org/danni/2014/02/02/a-libnss-plugin-for-docker/ http://blogs.gnome.org/danni/2014/02/02/a-libnss-plugin-for-... looks interesting too. I read the Jumper post thing when it was HN. I need to think about that some more.

ballard 13y ago

This is a pure marketing story pushing a bad solution. Hiera, a simple hierarchal property distribution system using a backend of Zookeeper plus puppet or chef is far superior. Etcd is the PHP of configuration management.

danieldk 13y ago
Wow. I know neither etcd or Hiera. But please provide some arguments against etcd if you think it is bad, rather than just bashing it. It would be interesting to know the cons and pros of both solutions.
- ballard 13y ago
  I'm bashing it because it oversimplifies the problem and claims to be a solution that doesn't address the irreducibility of the problem. It's great for a host file but scp can do that. It doesn't coordinate the transition of services to other states. Puppet does an incredible amount of work (dependency satisfaction) to get things where you want them to be. Configuration management is as much management order of operations as well as what files should contain what. There's not much separating the two because you have to usually change them between states. Chef does this to, but in a simpler way. Cfengine was a past attempt, but is really complicated double work of what runs on a server and what runs on a managed node.
  - rdtsc 13y ago
    > It doesn't coordinate the transition of services to other states. Can you be more specific? So to co-ordinate transitions what else would it need -- multi-key transactions? Surely you have good reason to jump in and criticize it so sharply...
    - ballard 13y ago
      Configuration management transactions. Puppet has the notion of stages. Yes because it's marketing an unproven technology as a solution when better things already exist. Someone I know from (OpsCode||Puppet) even further the recommendation of zk as basically the only proven consistent KVS. A better approach should be to do what other cloud shops have done and ship ZK appliances. Pushing new tech on customers is using them to beta test unproven tech, which is reinventing the wheel and risky.

vidarh 13y ago

The discovery mechanism looks clumsy to me. There's no way we'd rely on a public discovery service, for example. If we're going to hardcode configuration information - such as the URL of a discovery service that may or may not be up or reachable, we might as well hardcode the addresses of a few peers. And running a second etcd cluster to bring up the main one seems pointless. Either it's turtles all the way down, or you then need to hardcode config information for the second cluster, in which case it serves little purpose. I'd rather have a mechanism where each peer takes a list of possible peers and tries to connect, with a method for deciding when there is quorum to elect an initial leader and start allowing writes (that's easy enough by introducing a config option to decide if a peer is "blessed" to be part of the initial leadership election, and how many blessed peers must be connected to have quorum - just needs to be enough to form a majority of blessed peers to prevent more than one subset from electing a leader before they manage to connect) Am I missing something?

nl 13y ago
Quoting the post: In previous releases, a human had to pick a leader, pass a list of -peers to all of the followers and maintain that list going forward. Presumably that method is still there?
- robszumski 13y ago
  Yep, you can still hardcode a list of peers via flag or config file. I think you can even use both a peer list and a discovery token at the same time.
ballard 13y ago
This is why top-down, single-source of truth is mostly the best way for core infrastructure. No pun intended. It's important for some parts to not be infinitely reconfigurable or dynamic because it would create chaos and service dependency deadlock/DoS. Most people not running bare metal don't know the lessons of how and why things underneath are they way they are and the sensible limits what's possible. It's also more secure because if it's possible to dictate all of the service details, it's much easier to run a lean and locked-down infrastructure. CoreOS by itself looks great. More JEOS distros need to happen. Trying to bundle more unproven things just looks marketing led the product.

baghali 13y ago

Has anyone checked out serf http://www.serfdom.io/ http://www.serfdom.io/ if yes what are the pros and cons of etcd and serf?