jandeboevrie•4d
High Available Mosquitto MQTT on Kubernetesraymii.org
19 comments
  • zrail•5h

    To preface, I'm not a Kubernetes or Mosquitto expert by any means.

    I'm confused about one point. A k8s Service sends traffic to pods matching the selector that are in "Ready" state, so wouldn't you accomplish HA without the pseudocontroller by just putting both pods in the Service? The Mosquitto bridge mechanism is bi-directional so you're already getting data re-sync no matter where a client writes.

    edit: I'm also curious if you could use a headless service and use an init container on the secondary to set up the bridge to the primary by selecting the IP that isn't it's own.

    • jandeboevrie•4h

      > so wouldn't you accomplish HA without the pseudocontroller by just putting both pods in the Service?

      I'm not sure how fast that would be, the extra controller container is needed for the almost instant failover.

      Answering your second question, why not an init container in the secondary, because now we can scale that failover controller up over multiple nodes, if the node where the (fairly stateless) controller runs goes down, we'd still have to wait until k8s schedules another pod instead of almost instantly.

  • andrewfromx•6h

    when dealing with long lasting TCP connections, why add that extra layer of network complexity with k8s? I work for a big IoT company and we have 1.8M connections spread across 15 ec2 c8g.xlarge boxes. Not even using a NLB just round-robin DNS. Wrote our own broker with https://github.com/lesismal/nbio and use a packer .hcl file to make the AMI that each ec2 box boots. Using https://github.com/lesismal/llib/tree/master/std/crypto/tls to make nbio work with TLS.

    • stackskipton•3h

      Ops type here who deals with this around Kafka.

      It comes down to how much you use Kubernetes. At my company, just about everything is in Kubernetes except for databases which are hosted by Azure. So having random VMs means we need to get Ansible, SSH Keys and SOC2 compliance annoyance. So the workload effort to get VMs running may be higher than Kubernetes even if you have to put in extra hacks.

      • NewJazz•2h

        You don't need ansible if it is all packed into the Ami.

    • avianlyric•2h

      K8s itself doesn’t introduce any real additional network complexity, at least not vanilla k8s.

      At the end of the day, K8s only takes care of scheduling containers, and provides a super basic networking proxy layer for convenience. But there’s absolutely nothing in k8s that requires you use that proxy layer, or any other network overlay.

      You can easily setup pods that directly expose their ports on the node they’re running on, and have k8s services just provide the IPs of nodes running associated pods as a list. Then rely on either on clients to handle multiple addresses themselves (by picking an address at random, and failing over to another random address if needed), configure k8s DNS to provide DNS round robin, or put an NLB or something in front of it all.

      Everyone uses network overlays with k8s because it makes it easy for services in k8s to talk to other services in k8s. But there’s no requirement to force all your external inbound traffic through that layer. You can just use k8s to handle nodes, and collect needed meta-data for upstream clients to connect directly to services running on nodes with nothing but the container layer between the client and the running service.

      • andrewfromx•1h

        | Aspect | Direct EC2 (No K8s) | Kubernetes (K8s Pods) |

        |-------------------------|-------------------------------------------------------|-------------------------------------------------------------------------------------|

        | Networking Layers | Direct connection to EC2 instance (optional load balancer). | Service VIP → kube-proxy → CNI → pod (plus optional external load balancer). |

        | Load Balancing | Optional, handled by ELB/ALB or application. | Built-in via kube-proxy (iptables/IPVS) and Service. |

        | IP Addressing | Static or dynamic EC2 instance IP. | Pod IPs are dynamic, abstracted by Service VIP. |

        | Connection Persistence | Depends on application and OS TCP stack. | Depends on session affinity, graceful termination, and application reconnection logic. |

        | Overhead | Minimal (direct TCP). | Additional latency from kube-proxy, CNI, and load balancer. |

        | Resilience | Connection drops if instance fails. | Connection may drop if pod is rescheduled, but Kubernetes can reroute to new pods. |

        | Configuration Complexity| Simple (OS-level TCP tuning). | Complex (session affinity, PDBs, graceful termination, CNI tuning). |

  • oulipo•7h

    Wouldn't more modern implementations like EMQx be better suited for HA ?

    • jpgvm•6h

      I built a high scale MQTT ingestion system by utilising the MQTT protocol handler for Apache Pulsar (https://github.com/streamnative/mop). I ran a forked version and contributed back some of non-proprietary bits.

      A lot more work than Mosquitto but obviously HA/distributed and some tradeoffs w.r.t features. Worth it if you want to run Pulsar anyway for other reasons.

      • oulipo•2h

        I was going to go for Redpanda, what would be the pro/cons of Pulsar you think?

    • jandeboevrie•7h

      Would they work as performant and use the same amount of (less, almost nothing) resources? I've ran mosquito clusters with tens of thousands of connected clients, thousands of messages per second, on 2 cores and 2GB of ram, while mostly idling. (Without retention, using clean sessions and only QoS 0)...

    • bo0tzz•7h

      EMQX just locked HA/clustering behind a paywall: https://www.emqx.com/en/blog/adopting-business-source-licens...

      • zrail•7h

        Sigh that's annoying.

        Edit: it's not a paywall. It's the standard BSL with a 4 year Apache revert. I personally have zero issue with this.

        • bo0tzz•5h

          It is a paywall, clustering won't work unless you have a license key.

          • zrail•3h

            Yeah I see that now. Ugh.

        • casper14•6h

          Oh can you comment on what this means? I'm not too familiar with it. Thanks!

          • zrail•5h

            BSL is a source-available license that by default forbids production use. After a certain period after the date of any particular release, not to exceed four years, that release automatically converts to an open source license, typically the Apache license.

            Projects can add additional license grants to the base BSL. EMQX, for example, adds a grant for commercial production use of single-node installations, as well as production use for non-commercial applications.

    • seized•7h

      VerneMQ also has built in clustering and message replication which would make this easy.

      • oulipo•7h

        Have you tried both EMQx and VerneMQ and would you specifically recommend one over the other? I don't have experience with VerneMQ