8 ms·

Deploying PostgreSQL Clusters Using StatefulSets

164 points by TheIronYuppie 10y ago

TheIronYuppie 10y ago
Stateful Sets went to beta in Kubernetes 1.5 (in December) and we've been really excited to see so many applications get ported over. Please let me know if you have any questions! Disclosure: I work at Google on Kubernetes.
- lobster_johnson 10y ago
  Once this goes out of beta, would you say that running PostgreSQL on Kubernetes is now considered good practice? I've been wary of running anything stateful on K8s for other reasons than the stable identity stuff. Historically, Docker's I/O has not been particularly robust — well, Docker has not been particularly robust. You also have to be very careful about resource limits and requests. In particular, you have to ensure that the QoS class "Guaranteed" [1] kicks in, because the last thing you want is for Kubernetes to think that PostgreSQL is something that is happily rescheduled. [1] https://github.com/kubernetes/community/blob/master/contributors/design-proposals/resource-qos.md https://github.com/kubernetes/community/blob/master/contribu...
  - crb 10y ago
    I think I saw you on this thread, but I'd defer to Clayton Coleman of Red Hat/OpenShift in this post: https://news.ycombinator.com/item?id=13680244 https://news.ycombinator.com/item?id=13680244 tl;dr: do you want to be a DBA? do you want to be a cluster admin? If you want to be both you can run databases on Kubernetes. If you don't want to be a DBA, use a managed service.
    - lobster_johnson 10y ago
      Of course. But there's a difference between knowing that there are failure modes, and actually knowing them. Non-containerized environments (VMs, bare metal) are well-understood and fairly predictable; Docker and Kubernetes are moving targets. There are "known unknowns". As an example, I am involved in a project that uses continuous delivery for deploys, and we recently had an incident where the GKE node ran out of inodes because Docker was keeping all the layers of dead containers around. Kubernetes handles this correctly: Best-effort pods were evicted and the node went back to being ready once the inode use went down. PostgreSQL would have stayed up in this case, but it was still a little surprising that GKE, which is nominally managed, does not have a process in place for cleaning up Docker's garbage. (Edit: Apparently it's a bug [1].) When discussing Docker and Kubernetes, there are very often edge cases that come up. For example, until a couple of months ago, Kubernetes had a serious bug that would often cause the wrong network volume to be mounted to a new pod. You can be the world's best containerized-database admin and still be surprised by things like this, which have nothing to do with the nature of containers, and everything to do with the specifics of the software that controls them. [1] https://github.com/kubernetes/kubernetes/issues/41033 https://github.com/kubernetes/kubernetes/issues/41033
      - crb 10y ago
        You sound like you might be first in line to use a rkt-powered GKE :)
        lobster_johnson 10y ago
        I'm indeed hopeful that rkt is the way forward. There are too many competing, overlapping concerns between K8s and Docker.
        crb 10y ago
        https://twitter.com/chanezon/status/834847669042311168 https://twitter.com/chanezon/status/834847669042311168 "containerd is all we wanted from @docker in @kubernetesio and none of what we didn't need: kudos to the team!"
  - x0x0 10y ago
    May I ask why you want to run pg inside kubernetes? I'm trying to wrap my head around why that's a thing that people want to do.
    - atombender 10y ago
      If you have to maintain Kubernetes _and_ classical VMs, you have two overlapping systems. I'd rather just use one, and get the flexibility it brings over classical VMs. For example, I'd be able to upgrade by just starting another container and replicating into it, then routing traffic over. I'd retain the option of rolling back by routing traffic back if anything goes wrong. I'd be able to spin up/down redundant read-only replicas simply by changing the number of replicas. And other apps would be able to piggyback on Kubernetes' discovery system (typically you let service names resolve into IPs/SRV records through DNS). And so on. You can do anything you want with classical VMs, of course, it's just more static and slower: Provisioning another VM, configuring it (Puppet, Salt, Chef, etc.), connecting persistent storage, reconfiguring everything to point to the right places, configuring DNS, etc. In short: If you use Kubernetes as your orchestrator, why would you not want to use it for everything?
      - x0x0 10y ago
        I totally get the attraction of learning one set of tooling, rather than k8s and ami/homebrew. Blue/green deploys are nice, particularly because we deploy for most PRs. But it just seems like you're trying to shove a very stateful management problem (the schema, the associated storage) into a system designed for mostly stateless stuff. And that way lies a giant hassle. Plus we're certainly not at huge scale, but db rollbacks are nontrivial, and we have to be somewhat careful about schema modifications. Thanks for your comment!
        lobster_johnson 10y ago
        But Kubernetes _is_ designed to support stateful containers; that's what StatefulSets are about. There's nothing about containers that says they need to be stateless, it's just more convenient that way because you can treat every container as expendable, redundant, fungible commodities. But the real world needs state, and Kubernetes is capable of managing it. In particular, the pattern pretty much required for stateful apps on Kubernetes is that of using an exclusive-access network block device. Since only one container (or pod) can mount it at any given time, you can ensure that the state follows the container around.
- PaulJulius 10y ago
  This is unrelated to StatefulSets, but I'm going to take the opportunity to ask a Kubernetes engineer for help, since the the kubernetes-users Slack channel sort of feels like shouting into a void. We deploy a small cluster (1 master, 6 nodes) at our startup that started misbehaving last week. All of a sudden three of the nodes went down - one became unresponsive and two had the error "container runtime is down." We couldn't ssh into the unresponsive one, but according to AWS the machine was fine, still receiving network requests and using CPU. Since we couldn't diagnose the issue, we spun up an entirely new cluster using kops, but started seeing the exact same behavior later that night, and again over the weekend. Three nodes were in a not ready state, for the same reasons (unresponsive and container runtime is down). Right now our only solution to solve this issue is to manually terminate the EC2 instances and rely on the Auto-Scaling Group to create new ones. In the mean time, Kubernetes tells us that it can't schedule all of our desired pods, so half of our jobs aren't running, obviously an undesirable situation. A handful of questions I have about the situation: Why are these nodes going down? What causes a node to go unresponsive? Why does the container runtime go down on a node and why doesn't it get restarted? Why doesn't Kubernetes destroy these nodes when they've been out of commission for 3-4 hours? Any help would be appreciated!!! I've been looking through half a dozen log files and gotten zero answers.
  - crb 10y ago
    > Why doesn't Kubernetes destroy these nodes when they've been out of commission for 3-4 hours? Kubernetes isn't responsible for the lifecycle of its nodes. It can run in a DC where "destroying a node" might mean paging a tech to turn off a server. Something external - in your case, kops & your ASG - is responsible for the nodes that Kubernetes runs on. That's a deliberate design choice. It should make a correct decision not to schedule work there, which it sounds like it did. Given that, your other questions are hard to answer. kubelet is a process that runs on the nodes. So is docker. If you can't get into the machine to diagnose the fault, I'd encourage you to set up some monitoring/log shipping off the node so you can see what the state was when it failed. There's nothing inherently "Kubernetes" about this diagnosis - it's more EC2, node/kernel/OS and Docker troubleshooting, in that order.
    - 10y ago
danmaz74 10y ago
Slightly OT, but, from a quick glance at the post, it looks like the postgres data is persisted on a network file system. Does anybody have any experience with a big enough and this kind of configuration, and what is the performance compared with SSD local disks? Intuitively I wouldn't expect a networked disk to be a viable solution for postgres, but seeing it proposed like this makes me think that maybe my intuition was wrong...
- travem 10y ago
  There would no doubt be some performance differences between local and networked but it is very normal in enterprises to deploy databases on a SAN to take advantage of the array's data services. On the NAS side I believe Oracle also are often deployed on NetApp arrays, they use their own NFS client to ensure the DB isn't compromised by bad NFS client implementations.
- TheIronYuppie 10y ago
  QQ - how do you deal with the situation where a node goes away? GCP offers networked SSD, and performance is fairly good, but, as always, YMMV. Disclosure: I work at Google on Kubernetes
  - detaro 10y ago
    I think the posters point is that the article talks about using NFS or other shared network filesystems, not a block storage protocol?
- lobster_johnson 10y ago
  People have run Postgres on network disks — Elastic Block Storage (EBS) volumes on AWS, or Persistent Disks on Google Cloud — for a long time. They're implemented like a software SAN, with dedicated network paths, and throughput/latency is very good. Not as good as local, but still good enough for most apps. On Google Cloud, you do have to option of using a local SSD [1], but it comes with a bunch of limitations. It maxes out at 375GB (though you can allocate up to 8 per VM). They're somewhat expensive. They're not durable; if you stop the VM, the disk is lost. They're classified as "scratch disks" in the UI, which is a good indicator of their intended purpose. Edit: Using a networked file system, however, is a bad idea. [1] https://cloud.google.com/compute/docs/disks/local-ssd https://cloud.google.com/compute/docs/disks/local-ssd
deleted 10y ago
[deleted]
sandGorgon 10y ago
Here's a quick question - isn't StatefulSets and PersistentVolumeClaim the exact opposite of how fault tolerant database systems are generally built ? The kubernetes StatefulSets project is actually trying to build a usecase for Postgresql-on-s3. I think its the wrong abstraction to go after in most usecases for database systems including things like ElasticSearch. I dont think that even Aurora is trying to solve this using persistent storage. You dont really care about solving underlying persistence... you make the whole system fault tolerant : which includes high availability, failover, etc. IMHO kubernetes still has problems in orchestrating an ElasticSearch/Zookeeper cluster for high availability. The problem of discovery, load balancing, etc are bottlenecks.
- alexk 10y ago
  > Here's a quick question - isn't StatefulSets and PersistentVolumeClaim the exact opposite of how fault tolerant database systems are generally built ? In some cases it is perfectly valid to rely on underlying storage to get HA. E.g. RDS relies on EBS https://aws.amazon.com/message/65648/ https://aws.amazon.com/message/65648/ > IMHO kubernetes still has problems in orchestrating an ElasticSearch/Zookeeper cluster for high availability I don't think that is the case any more. It is not trivial to build a proper automation on top of K8s, but possible, here is an example of a complex distributed DB deployed on top of Kubernetes: https://github.com/coreos/etcd-operator https://github.com/coreos/etcd-operator There are many challenges, but they are not specific to Kubernetes, rather than just automating the deployment of such complex systems is generally hard.
  - markonen 10y ago
    As your link illustrates, Multi-AZ is the only real HA option for RDS PostgreSQL, and it doesn't share storage between nodes. So even though RDS uses EBS, you can't really say it is the underlying storage layer that provides RDS's high availability.
  - sandGorgon 10y ago
    Thanks for pointing out the Operator framework. Please correct me if I am wrong, but Operator is not a Kubernetes thing - its a custom functionality built by coreos. It is undoubtedly awesome, but it is very hard to get it working on non coreos distro. I personally believe that orchestration primitives like operators, linkerd, ingress, etc are what the k8s project should focus on. Im actually unsure if StatefulSets are solving production problems for anybody. IMHO they are a fairly Googley concept and hard to apply outside of Google for anybody (without solving the networked filesystem problem first).
alexk 10y ago
If you are interested in deployments of databases on top of cluster orchestrators, here are some interesting projects: * Postgres automation for Kubernetes deployments https://github.com/sorintlab/stolon https://github.com/sorintlab/stolon * Automation for operating the Etcd cluster:https://github.com/coreos/etcd-operator https://github.com/coreos/etcd-operator * Kubernetes-native deployment of Ceph: https://rook.io/ https://rook.io/
- foxylion 10y ago
  Thanks for the links. Do you know about a project that Targets PostgreSQL as a operator, like etcd?
  - alexk 10y ago
    This one: https://github.com/sorintlab/stolon https://github.com/sorintlab/stolon It is not called the operator, but in many ways it is similar to what Etcd Operator does
    - crb 10y ago
      If your pattern requires you to connect to etcd, then you're not taking the best advantage of Kubernetes. Yes, you can connect to an etcd instance outside of Kubernetes, or deploy etcd on Kubernetes. CoreOS developed the etcd operator for the purposes of self-hosting the system KV store, but you can of course run a "user" etcd. A better pattern is relying on the objects provided by Kubernetes, which are themselves backed by a lock service (which happens to be etcd, but that's an implementation detail you shouldn't worry about.) You could, for example, use an Annotation on an object to do leader election. Look at how HA masters are implemented on Kubernetes, for example: https://github.com/kubernetes/kubernetes/blob/master/pkg/client/leaderelection/leaderelection.go https://github.com/kubernetes/kubernetes/blob/master/pkg/cli...
      - achanda358 10y ago
        That's a great point. But doesn't this make it mandatory for the applications to use Go? It would have been more useful if there was a REST interface for leader election.
kitallis 10y ago
There's also https://github.com/staples-sparx/Agrajag https://github.com/staples-sparx/Agrajag which I've been working on. It is an abstraction on top of repmgr and repmgrd. It relies on repmgrd for quorum and uses zookeeper as a distributed store for who the new master is. This way your apps/bouncer/HAProxy can read off of it. It does not use zk for leader election and relies on repmgrd for that. It's a move away from the normal repmgrd style of push notifications to a pull + broadcast mechanism. This allows many nodes to broadcast the same information (increasing the surface area of success) and fencing old masters. repmgr and repmgrd are written by core contributors of postgres and this is just an orchestration layer (with built-in monitoring) on top of it. It's very much under development at the moment. More details are here: https://github.com/staples-sparx/Agrajag/blob/dev/doc/tradeoffs.md https://github.com/staples-sparx/Agrajag/blob/dev/doc/tradeo... There are plans to add more lines of defense in cases where repmgrd dies. I'll be speaking about it a bit this week at pgconf.in if anyone's interested: http://pgconf.in/schedule/a-postgres-orchestra/ http://pgconf.in/schedule/a-postgres-orchestra/

164 points by TheIronYuppie 10y ago

Stateful Sets went to beta in Kubernetes 1.5 (in December) and we've been really excited to see so many applications get ported over. Please let me know if you have any questions! Disclosure: I work at Google on Kubernetes.

lobster_johnson 10y ago
Once this goes out of beta, would you say that running PostgreSQL on Kubernetes is now considered good practice? I've been wary of running anything stateful on K8s for other reasons than the stable identity stuff. Historically, Docker's I/O has not been particularly robust — well, Docker has not been particularly robust. You also have to be very careful about resource limits and requests. In particular, you have to ensure that the QoS class "Guaranteed" [1] kicks in, because the last thing you want is for Kubernetes to think that PostgreSQL is something that is happily rescheduled. [1] https://github.com/kubernetes/community/blob/master/contributors/design-proposals/resource-qos.md https://github.com/kubernetes/community/blob/master/contribu...
- crb 10y ago
  I think I saw you on this thread, but I'd defer to Clayton Coleman of Red Hat/OpenShift in this post: https://news.ycombinator.com/item?id=13680244 https://news.ycombinator.com/item?id=13680244 tl;dr: do you want to be a DBA? do you want to be a cluster admin? If you want to be both you can run databases on Kubernetes. If you don't want to be a DBA, use a managed service.
  - lobster_johnson 10y ago
    Of course. But there's a difference between knowing that there are failure modes, and actually knowing them. Non-containerized environments (VMs, bare metal) are well-understood and fairly predictable; Docker and Kubernetes are moving targets. There are "known unknowns". As an example, I am involved in a project that uses continuous delivery for deploys, and we recently had an incident where the GKE node ran out of inodes because Docker was keeping all the layers of dead containers around. Kubernetes handles this correctly: Best-effort pods were evicted and the node went back to being ready once the inode use went down. PostgreSQL would have stayed up in this case, but it was still a little surprising that GKE, which is nominally managed, does not have a process in place for cleaning up Docker's garbage. (Edit: Apparently it's a bug [1].) When discussing Docker and Kubernetes, there are very often edge cases that come up. For example, until a couple of months ago, Kubernetes had a serious bug that would often cause the wrong network volume to be mounted to a new pod. You can be the world's best containerized-database admin and still be surprised by things like this, which have nothing to do with the nature of containers, and everything to do with the specifics of the software that controls them. [1] https://github.com/kubernetes/kubernetes/issues/41033 https://github.com/kubernetes/kubernetes/issues/41033
    - crb 10y ago
      You sound like you might be first in line to use a rkt-powered GKE :)
      - lobster_johnson 10y ago
        I'm indeed hopeful that rkt is the way forward. There are too many competing, overlapping concerns between K8s and Docker.
        crb 10y ago
        https://twitter.com/chanezon/status/834847669042311168 https://twitter.com/chanezon/status/834847669042311168 "containerd is all we wanted from @docker in @kubernetesio and none of what we didn't need: kudos to the team!"
- x0x0 10y ago
  May I ask why you want to run pg inside kubernetes? I'm trying to wrap my head around why that's a thing that people want to do.
  - atombender 10y ago
    If you have to maintain Kubernetes _and_ classical VMs, you have two overlapping systems. I'd rather just use one, and get the flexibility it brings over classical VMs. For example, I'd be able to upgrade by just starting another container and replicating into it, then routing traffic over. I'd retain the option of rolling back by routing traffic back if anything goes wrong. I'd be able to spin up/down redundant read-only replicas simply by changing the number of replicas. And other apps would be able to piggyback on Kubernetes' discovery system (typically you let service names resolve into IPs/SRV records through DNS). And so on. You can do anything you want with classical VMs, of course, it's just more static and slower: Provisioning another VM, configuring it (Puppet, Salt, Chef, etc.), connecting persistent storage, reconfiguring everything to point to the right places, configuring DNS, etc. In short: If you use Kubernetes as your orchestrator, why would you not want to use it for everything?
    - x0x0 10y ago
      I totally get the attraction of learning one set of tooling, rather than k8s and ami/homebrew. Blue/green deploys are nice, particularly because we deploy for most PRs. But it just seems like you're trying to shove a very stateful management problem (the schema, the associated storage) into a system designed for mostly stateless stuff. And that way lies a giant hassle. Plus we're certainly not at huge scale, but db rollbacks are nontrivial, and we have to be somewhat careful about schema modifications. Thanks for your comment!
      - lobster_johnson 10y ago
        But Kubernetes _is_ designed to support stateful containers; that's what StatefulSets are about. There's nothing about containers that says they need to be stateless, it's just more convenient that way because you can treat every container as expendable, redundant, fungible commodities. But the real world needs state, and Kubernetes is capable of managing it. In particular, the pattern pretty much required for stateful apps on Kubernetes is that of using an exclusive-access network block device. Since only one container (or pod) can mount it at any given time, you can ensure that the state follows the container around.
PaulJulius 10y ago
This is unrelated to StatefulSets, but I'm going to take the opportunity to ask a Kubernetes engineer for help, since the the kubernetes-users Slack channel sort of feels like shouting into a void. We deploy a small cluster (1 master, 6 nodes) at our startup that started misbehaving last week. All of a sudden three of the nodes went down - one became unresponsive and two had the error "container runtime is down." We couldn't ssh into the unresponsive one, but according to AWS the machine was fine, still receiving network requests and using CPU. Since we couldn't diagnose the issue, we spun up an entirely new cluster using kops, but started seeing the exact same behavior later that night, and again over the weekend. Three nodes were in a not ready state, for the same reasons (unresponsive and container runtime is down). Right now our only solution to solve this issue is to manually terminate the EC2 instances and rely on the Auto-Scaling Group to create new ones. In the mean time, Kubernetes tells us that it can't schedule all of our desired pods, so half of our jobs aren't running, obviously an undesirable situation. A handful of questions I have about the situation: Why are these nodes going down? What causes a node to go unresponsive? Why does the container runtime go down on a node and why doesn't it get restarted? Why doesn't Kubernetes destroy these nodes when they've been out of commission for 3-4 hours? Any help would be appreciated!!! I've been looking through half a dozen log files and gotten zero answers.
- crb 10y ago
  > Why doesn't Kubernetes destroy these nodes when they've been out of commission for 3-4 hours? Kubernetes isn't responsible for the lifecycle of its nodes. It can run in a DC where "destroying a node" might mean paging a tech to turn off a server. Something external - in your case, kops & your ASG - is responsible for the nodes that Kubernetes runs on. That's a deliberate design choice. It should make a correct decision not to schedule work there, which it sounds like it did. Given that, your other questions are hard to answer. kubelet is a process that runs on the nodes. So is docker. If you can't get into the machine to diagnose the fault, I'd encourage you to set up some monitoring/log shipping off the node so you can see what the state was when it failed. There's nothing inherently "Kubernetes" about this diagnosis - it's more EC2, node/kernel/OS and Docker troubleshooting, in that order.
  - 10y ago

danmaz74 10y ago

Slightly OT, but, from a quick glance at the post, it looks like the postgres data is persisted on a network file system. Does anybody have any experience with a big enough and this kind of configuration, and what is the performance compared with SSD local disks? Intuitively I wouldn't expect a networked disk to be a viable solution for postgres, but seeing it proposed like this makes me think that maybe my intuition was wrong...

travem 10y ago
There would no doubt be some performance differences between local and networked but it is very normal in enterprises to deploy databases on a SAN to take advantage of the array's data services. On the NAS side I believe Oracle also are often deployed on NetApp arrays, they use their own NFS client to ensure the DB isn't compromised by bad NFS client implementations.
TheIronYuppie 10y ago
QQ - how do you deal with the situation where a node goes away? GCP offers networked SSD, and performance is fairly good, but, as always, YMMV. Disclosure: I work at Google on Kubernetes
- detaro 10y ago
  I think the posters point is that the article talks about using NFS or other shared network filesystems, not a block storage protocol?
lobster_johnson 10y ago
People have run Postgres on network disks — Elastic Block Storage (EBS) volumes on AWS, or Persistent Disks on Google Cloud — for a long time. They're implemented like a software SAN, with dedicated network paths, and throughput/latency is very good. Not as good as local, but still good enough for most apps. On Google Cloud, you do have to option of using a local SSD [1], but it comes with a bunch of limitations. It maxes out at 375GB (though you can allocate up to 8 per VM). They're somewhat expensive. They're not durable; if you stop the VM, the disk is lost. They're classified as "scratch disks" in the UI, which is a good indicator of their intended purpose. Edit: Using a networked file system, however, is a bad idea. [1] https://cloud.google.com/compute/docs/disks/local-ssd https://cloud.google.com/compute/docs/disks/local-ssd

deleted 10y ago

[deleted]

sandGorgon 10y ago

Here's a quick question - isn't StatefulSets and PersistentVolumeClaim the exact opposite of how fault tolerant database systems are generally built ? The kubernetes StatefulSets project is actually trying to build a usecase for Postgresql-on-s3. I think its the wrong abstraction to go after in most usecases for database systems including things like ElasticSearch. I dont think that even Aurora is trying to solve this using persistent storage. You dont really care about solving underlying persistence... you make the whole system fault tolerant : which includes high availability, failover, etc. IMHO kubernetes still has problems in orchestrating an ElasticSearch/Zookeeper cluster for high availability. The problem of discovery, load balancing, etc are bottlenecks.

alexk 10y ago
> Here's a quick question - isn't StatefulSets and PersistentVolumeClaim the exact opposite of how fault tolerant database systems are generally built ? In some cases it is perfectly valid to rely on underlying storage to get HA. E.g. RDS relies on EBS https://aws.amazon.com/message/65648/ https://aws.amazon.com/message/65648/ > IMHO kubernetes still has problems in orchestrating an ElasticSearch/Zookeeper cluster for high availability I don't think that is the case any more. It is not trivial to build a proper automation on top of K8s, but possible, here is an example of a complex distributed DB deployed on top of Kubernetes: https://github.com/coreos/etcd-operator https://github.com/coreos/etcd-operator There are many challenges, but they are not specific to Kubernetes, rather than just automating the deployment of such complex systems is generally hard.
- markonen 10y ago
  As your link illustrates, Multi-AZ is the only real HA option for RDS PostgreSQL, and it doesn't share storage between nodes. So even though RDS uses EBS, you can't really say it is the underlying storage layer that provides RDS's high availability.
- sandGorgon 10y ago
  Thanks for pointing out the Operator framework. Please correct me if I am wrong, but Operator is not a Kubernetes thing - its a custom functionality built by coreos. It is undoubtedly awesome, but it is very hard to get it working on non coreos distro. I personally believe that orchestration primitives like operators, linkerd, ingress, etc are what the k8s project should focus on. Im actually unsure if StatefulSets are solving production problems for anybody. IMHO they are a fairly Googley concept and hard to apply outside of Google for anybody (without solving the networked filesystem problem first).

alexk 10y ago

If you are interested in deployments of databases on top of cluster orchestrators, here are some interesting projects: * Postgres automation for Kubernetes deployments https://github.com/sorintlab/stolon https://github.com/sorintlab/stolon * Automation for operating the Etcd cluster:https://github.com/coreos/etcd-operator https://github.com/coreos/etcd-operator * Kubernetes-native deployment of Ceph: https://rook.io/ https://rook.io/

foxylion 10y ago
Thanks for the links. Do you know about a project that Targets PostgreSQL as a operator, like etcd?
- alexk 10y ago
  This one: https://github.com/sorintlab/stolon https://github.com/sorintlab/stolon It is not called the operator, but in many ways it is similar to what Etcd Operator does
  - crb 10y ago
    If your pattern requires you to connect to etcd, then you're not taking the best advantage of Kubernetes. Yes, you can connect to an etcd instance outside of Kubernetes, or deploy etcd on Kubernetes. CoreOS developed the etcd operator for the purposes of self-hosting the system KV store, but you can of course run a "user" etcd. A better pattern is relying on the objects provided by Kubernetes, which are themselves backed by a lock service (which happens to be etcd, but that's an implementation detail you shouldn't worry about.) You could, for example, use an Annotation on an object to do leader election. Look at how HA masters are implemented on Kubernetes, for example: https://github.com/kubernetes/kubernetes/blob/master/pkg/client/leaderelection/leaderelection.go https://github.com/kubernetes/kubernetes/blob/master/pkg/cli...
    - achanda358 10y ago
      That's a great point. But doesn't this make it mandatory for the applications to use Go? It would have been more useful if there was a REST interface for leader election.

kitallis 10y ago

There's also https://github.com/staples-sparx/Agrajag https://github.com/staples-sparx/Agrajag which I've been working on. It is an abstraction on top of repmgr and repmgrd. It relies on repmgrd for quorum and uses zookeeper as a distributed store for who the new master is. This way your apps/bouncer/HAProxy can read off of it. It does not use zk for leader election and relies on repmgrd for that. It's a move away from the normal repmgrd style of push notifications to a pull + broadcast mechanism. This allows many nodes to broadcast the same information (increasing the surface area of success) and fencing old masters. repmgr and repmgrd are written by core contributors of postgres and this is just an orchestration layer (with built-in monitoring) on top of it. It's very much under development at the moment. More details are here: https://github.com/staples-sparx/Agrajag/blob/dev/doc/tradeoffs.md https://github.com/staples-sparx/Agrajag/blob/dev/doc/tradeo... There are plans to add more lines of defense in cases where repmgrd dies. I'll be speaking about it a bit this week at pgconf.in if anyone's interested: http://pgconf.in/schedule/a-postgres-orchestra/ http://pgconf.in/schedule/a-postgres-orchestra/