Tuesday, August 02, 2016
Challenges of a Remotely Managed, On-Premises, Bare-Metal Kubernetes Cluster
Today’s post is written by Bich Le, chief architect at Platform9, describing how their engineering team overcame challenges in remotely managing bare-metal Kubernetes clusters.
Introduction
The recently announced Platform9 Managed Kubernetes (PMK) is an on-premises enterprise Kubernetes solution with an unusual twist: while clusters run on a user’s internal hardware, their provisioning, monitoring, troubleshooting and overall life cycle is managed remotely from the Platform9 SaaS application. While users love the intuitive experience and ease of use of this deployment model, this approach poses interesting technical challenges. In this article, we will first describe the motivation and deployment architecture of PMK, and then present an overview of the technical challenges we faced and how our engineering team addressed them.
Multi-OS bootstrap model
Like its predecessor, Managed OpenStack, PMK aims to make it as easy as possible for an enterprise customer to deploy and operate a “private cloud”, which, in the current context, means one or more Kubernetes clusters. To accommodate customers who standardize on a specific Linux distro, our installation process uses a “bare OS” or “bring your own OS” model, which means that an administrator deploys PMK to existing Linux nodes by installing a simple RPM or Deb package on their favorite OS (Ubuntu-14, CentOS-7, or RHEL-7). The package, which the administrator downloads from their Platform9 SaaS portal, starts an agent which is preconfigured with all the information and credentials needed to securely connect to and register itself with the customer’s Platform9 SaaS controller running on the WAN.
Node management
The first challenge was configuring Kubernetes nodes in the absence of a bare-metal cloud API and SSH access into nodes. We solved it using the node pool concept and configuration management techniques. Every node running the agent automatically shows up in the SaaS portal, which allows the user to authorize the node for use with Kubernetes. A newly authorized node automatically enters a node pool, indicating that it is available but not used in any clusters. Independently, the administrator can create one or more Kubernetes clusters, which start out empty. At any later time, he or she can request one or more nodes to be attached to any cluster. PMK fulfills the request by transferring the specified number of nodes from the pool to the cluster. When a node is authorized, its agent becomes a configuration management agent, polling for instructions from a CM server running in the SaaS application and capable of downloading and configuring software.
Cluster creation and node attach/detach operations are exposed to administrators via a REST API, a CLI utility named qb, and the SaaS-based Web UI. The following screenshot shows the Web UI displaying one 3-node cluster named clus100, one empty cluster clus101, and the three nodes.
Cluster initialization
The first time one or more nodes are attached to a cluster, PMK configures the nodes to form a complete Kubernetes cluster. Currently, PMK automatically decides the number and placement of Master and Worker nodes. In the future, PMK will give administrators an “advanced mode” option allowing them to override and customize those decisions. Through the CM server, PMK then sends to each node a configuration and a set of scripts to initialize each node according to the configuration. This includes installing or upgrading Docker to the required version; starting 2 docker daemons (bootstrap and main), creating the etcd K/V store, establishing the flannel network layer, starting kubelet, and running the Kubernetes appropriate for the node’s role (master vs. worker). The following diagram shows the component layout of a fully formed cluster.
Containerized kubelet?
Another hurdle we encountered resulted from our original decision to run kubelet as recommended by the Multi-node Docker Deployment Guide. We discovered that this approach introduces complexities that led to many difficult-to-troubleshoot bugs that were sensitive to the combined versions of Kubernetes, Docker, and the node OS. Example: kubelet’s need to mount directories containing secrets into containers to support the Service Accounts mechanism. It turns out that doing this from inside of a container is tricky, and requires a complex sequence of steps that turned out to be fragile. After fixing a continuing stream of issues, we finally decided to run kubelet as a native program on the host OS, resulting in significantly better stability.
Overcoming networking hurdles
The Beta release of PMK currently uses flannel with UDP back-end for the network layer. In a Kubernetes cluster, many infrastructure services need to communicate across nodes using a variety of ports (443, 4001, etc..) and protocols (TCP and UDP). Often, customer nodes intentionally or unintentionally block some or all of the traffic, or run existing services that conflict with the required ports, resulting in non-obvious failures. To address this, we try to detect configuration problems early and inform the administrator immediately. PMK runs a “preflight” check on all nodes participating in a cluster before installing the Kubernetes software. This means running small test programs on each node to verify that (1) the required ports are available for binding and listening; and (2) nodes can connect to each other using all required ports and protocols. These checks run in parallel and take less than a couple of seconds before cluster initialization.
Monitoring
One of the values of a SaaS-managed private cloud is constant monitoring and early detection of problems by the SaaS team. Issues that can be addressed without intervention by the customer are handled automatically, while others trigger proactive communication with the customer via UI alerts, email, or real-time channels. Kubernetes monitoring is a huge topic worthy of its own blog post, so we’ll just briefly touch upon it. We broadly classify the problem into layers: (1) hardware & OS, (2) Kubernetes core (e.g. API server, controllers and kubelets), (3) add-ons (e.g. SkyDNS & ServiceLoadbalancer) and (4) applications. We are currently focused on layers 1-3. A major source of issues we’ve seen is add-on failures. If either DNS or the ServiceLoadbalancer reverse http proxy (soon to be upgraded to an Ingress Controller) fails, application services will start failing. One way we detect such failures is by monitoring the components using the Kubernetes API itself, which is proxied into the SaaS controller, allowing the PMK support team to monitor any cluster resource. To detect service failure, one metric we pay attention to is pod restarts. A high restart count indicates that a service is continually failing.
Future topics
We faced complex challenges in other areas that deserve their own posts: (1) Authentication and authorization with Keystone, the identity manager used by Platform9 products; (2) Software upgrades, i.e. how to make them brief and non-disruptive to applications; and (3) Integration with customer’s external load-balancers (in the absence of good automation APIs).
Conclusion
Platform9 Managed Kubernetes uses a SaaS-managed model to try to hide the complexity of deploying, operating and maintaining bare-metal Kubernetes clusters in customers’ data centers. These requirements led to the development of a unique cluster deployment and management architecture, which in turn led to unique technical challenges.This article described an overview of some of those challenges and how we solved them. For more information on the motivation behind PMK, feel free to view Madhura Maskasky’s blog post.
–Bich Le, Chief Architect, Platform9
- Introducing kustomize; Template-free Configuration Customization for Kubernetes May 29
- Getting to Know Kubevirt May 22
- Gardener - The Kubernetes Botanist May 17
- Docs are Migrating from Jekyll to Hugo May 5
- Announcing Kubeflow 0.1 May 4
- Current State of Policy in Kubernetes May 2
- Developing on Kubernetes May 1
- Zero-downtime Deployment in Kubernetes with Jenkins Apr 30
- Kubernetes Community - Top of the Open Source Charts in 2017 Apr 25
- Local Persistent Volumes for Kubernetes Goes Beta Apr 13
- Container Storage Interface (CSI) for Kubernetes Goes Beta Apr 10
- Fixing the Subpath Volume Vulnerability in Kubernetes Apr 4
- Principles of Container-based Application Design Mar 15
- Expanding User Support with Office Hours Mar 14
- How to Integrate RollingUpdate Strategy for TPR in Kubernetes Mar 13
- Apache Spark 2.3 with Native Kubernetes Support Mar 6
- Kubernetes: First Beta Version of Kubernetes 1.10 is Here Mar 2
- Reporting Errors from Control Plane to Applications Using Kubernetes Events Jan 25
- Core Workloads API GA Jan 15
- Introducing client-go version 6 Jan 12
- Extensible Admission is Beta Jan 11
- Introducing Container Storage Interface (CSI) Alpha for Kubernetes Jan 10
- Kubernetes v1.9 releases beta support for Windows Server Containers Jan 9
- Five Days of Kubernetes 1.9 Jan 8
- Introducing Kubeflow - A Composable, Portable, Scalable ML Stack Built for Kubernetes Dec 21
- Kubernetes 1.9: Apps Workloads GA and Expanded Ecosystem Dec 15
- Using eBPF in Kubernetes Dec 7
- PaddlePaddle Fluid: Elastic Deep Learning on Kubernetes Dec 6
- Autoscaling in Kubernetes Nov 17
- Certified Kubernetes Conformance Program: Launch Celebration Round Up Nov 16
- Kubernetes is Still Hard (for Developers) Nov 15
- Securing Software Supply Chain with Grafeas Nov 3
- Containerd Brings More Container Runtime Options for Kubernetes Nov 2
- Kubernetes the Easy Way Nov 1
- Enforcing Network Policies in Kubernetes Oct 30
- Using RBAC, Generally Available in Kubernetes v1.8 Oct 28
- It Takes a Village to Raise a Kubernetes Oct 26
- kubeadm v1.8 Released: Introducing Easy Upgrades for Kubernetes Clusters Oct 25
- Five Days of Kubernetes 1.8 Oct 24
- Introducing Software Certification for Kubernetes Oct 19
- Request Routing and Policy Management with the Istio Service Mesh Oct 10
- Kubernetes Community Steering Committee Election Results Oct 5
- Kubernetes 1.8: Security, Workloads and Feature Depth Sep 29
- Kubernetes StatefulSets & DaemonSets Updates Sep 27
- Introducing the Resource Management Working Group Sep 21
- Windows Networking at Parity with Linux for Kubernetes Sep 8
- Kubernetes Meets High-Performance Computing Aug 22
- High Performance Networking with EC2 Virtual Private Clouds Aug 11
- Kompose Helps Developers Move Docker Compose Files to Kubernetes Aug 10
- Happy Second Birthday: A Kubernetes Retrospective Jul 28
- How Watson Health Cloud Deploys Applications with Kubernetes Jul 14
- Kubernetes 1.7: Security Hardening, Stateful Application Updates and Extensibility Jun 30
- Draft: Kubernetes container development made easy May 31
- Managing microservices with the Istio service mesh May 31
- Kubespray Ansible Playbooks foster Collaborative Kubernetes Ops May 19
- Kubernetes: a monitoring guide May 19
- Dancing at the Lip of a Volcano: The Kubernetes Security Process - Explained May 18
- How Bitmovin is Doing Multi-Stage Canary Deployments with Kubernetes in the Cloud and On-Prem Apr 21
- RBAC Support in Kubernetes Apr 6
- Configuring Private DNS Zones and Upstream Nameservers in Kubernetes Apr 4
- Advanced Scheduling in Kubernetes Mar 31
- Scalability updates in Kubernetes 1.6: 5,000 node and 150,000 pod clusters Mar 30
- Five Days of Kubernetes 1.6 Mar 29
- Dynamic Provisioning and Storage Classes in Kubernetes Mar 29
- Kubernetes 1.6: Multi-user, Multi-workloads at Scale Mar 28
- The K8sPort: Engaging Kubernetes Community One Activity at a Time Mar 24
- Deploying PostgreSQL Clusters using StatefulSets Feb 24
- Containers as a Service, the foundation for next generation PaaS Feb 21
- Inside JD.com's Shift to Kubernetes from OpenStack Feb 10
- Run Deep Learning with PaddlePaddle on Kubernetes Feb 8
- Highly Available Kubernetes Clusters Feb 2
- Running MongoDB on Kubernetes with StatefulSets Jan 30
- Fission: Serverless Functions as a Service for Kubernetes Jan 30
- How we run Kubernetes in Kubernetes aka Kubeception Jan 20
- Scaling Kubernetes deployments with Policy-Based Networking Jan 19
- A Stronger Foundation for Creating and Managing Kubernetes Clusters Jan 12
- Kubernetes UX Survey Infographic Jan 9
- Kubernetes supports OpenAPI Dec 23
- Cluster Federation in Kubernetes 1.5 Dec 22
- Windows Server Support Comes to Kubernetes Dec 21
- StatefulSet: Run and Scale Stateful Applications Easily in Kubernetes Dec 20
- Introducing Container Runtime Interface (CRI) in Kubernetes Dec 19
- Five Days of Kubernetes 1.5 Dec 19
- Kubernetes 1.5: Supporting Production Workloads Dec 13
- From Network Policies to Security Policies Dec 8
- Kompose: a tool to go from Docker-compose to Kubernetes Nov 22
- Kubernetes Containers Logging and Monitoring with Sematext Nov 18
- Visualize Kubelet Performance with Node Dashboard Nov 17
- CNCF Partners With The Linux Foundation To Launch New Kubernetes Certification, Training and Managed Service Provider Program Nov 8
- Modernizing the Skytap Cloud Micro-Service Architecture with Kubernetes Nov 7
- Bringing Kubernetes Support to Azure Container Service Nov 7
- Tail Kubernetes with Stern Oct 31
- Introducing Kubernetes Service Partners program and a redesigned Partners page Oct 31
- How We Architected and Run Kubernetes on OpenStack at Scale at Yahoo! JAPAN Oct 24
- Building Globally Distributed Services using Kubernetes Cluster Federation Oct 14
- Helm Charts: making it simple to package and deploy common applications on Kubernetes Oct 10
- Dynamic Provisioning and Storage Classes in Kubernetes Oct 7
- How we improved Kubernetes Dashboard UI in 1.4 for your production needs Oct 3
- How we made Kubernetes insanely easy to install Sep 28
- How Qbox Saved 50% per Month on AWS Bills Using Kubernetes and Supergiant Sep 27
- Kubernetes 1.4: Making it easy to run on Kubernetes anywhere Sep 26
- High performance network policies in Kubernetes clusters Sep 21
- Creating a PostgreSQL Cluster using Helm Sep 9
- Deploying to Multiple Kubernetes Clusters with kit Sep 6
- Cloud Native Application Interfaces Sep 1
- Security Best Practices for Kubernetes Deployment Aug 31
- Scaling Stateful Applications using Kubernetes Pet Sets and FlexVolumes with Datera Elastic Data Fabric Aug 29
- SIG Apps: build apps for and operate them in Kubernetes Aug 16
- Kubernetes Namespaces: use cases and insights Aug 16
- Create a Couchbase cluster using Kubernetes Aug 15
- Challenges of a Remotely Managed, On-Premises, Bare-Metal Kubernetes Cluster Aug 2
- Why OpenStack's embrace of Kubernetes is great for both communities Jul 26
- The Bet on Kubernetes, a Red Hat Perspective Jul 21
- Happy Birthday Kubernetes. Oh, the places you’ll go! Jul 21
- A Very Happy Birthday Kubernetes Jul 21
- Bringing End-to-End Kubernetes Testing to Azure (Part 2) Jul 18
- Steering an Automation Platform at Wercker with Kubernetes Jul 15
- Dashboard - Full Featured Web Interface for Kubernetes Jul 15
- Cross Cluster Services - Achieving Higher Availability for your Kubernetes Applications Jul 14
- Citrix + Kubernetes = A Home Run Jul 14
- Thousand Instances of Cassandra using Kubernetes Pet Set Jul 13
- Stateful Applications in Containers!? Kubernetes 1.3 Says “Yes!” Jul 13
- Kubernetes in Rancher: the further evolution Jul 12
- Autoscaling in Kubernetes Jul 12
- rktnetes brings rkt container engine to Kubernetes Jul 11
- Minikube: easily run Kubernetes locally Jul 11
- Five Days of Kubernetes 1.3 Jul 11
- Updates to Performance and Scalability in Kubernetes 1.3 -- 2,000 node 60,000 pod clusters Jul 7
- Kubernetes 1.3: Bridging Cloud Native and Enterprise Workloads Jul 6
- Container Design Patterns Jun 21
- The Illustrated Children's Guide to Kubernetes Jun 9
- Bringing End-to-End Kubernetes Testing to Azure (Part 1) Jun 6
- Hypernetes: Bringing Security and Multi-tenancy to Kubernetes May 24
- CoreOS Fest 2016: CoreOS and Kubernetes Community meet in Berlin (& San Francisco) May 3
- Introducing the Kubernetes OpenStack Special Interest Group Apr 22
- SIG-UI: the place for building awesome user interfaces for Kubernetes Apr 20
- SIG-ClusterOps: Promote operability and interoperability of Kubernetes clusters Apr 19
- SIG-Networking: Kubernetes Network Policy APIs Coming in 1.3 Apr 18
- How to deploy secure, auditable, and reproducible Kubernetes clusters on AWS Apr 15
- Container survey results - March 2016 Apr 8
- Adding Support for Kubernetes in Rancher Apr 8
- Configuration management with Containers Apr 4
- Using Deployment objects with Kubernetes 1.2 Apr 1
- Kubernetes 1.2 and simplifying advanced networking with Ingress Mar 31
- Using Spark and Zeppelin to process big data on Kubernetes 1.2 Mar 30
- Building highly available applications using Kubernetes new multi-zone clusters (a.k.a. 'Ubernetes Lite') Mar 29
- AppFormix: Helping Enterprises Operationalize Kubernetes Mar 29
- How container metadata changes your point of view Mar 28
- Five Days of Kubernetes 1.2 Mar 28
- 1000 nodes and beyond: updates to Kubernetes performance and scalability in 1.2 Mar 28
- Scaling neural network image classification using Kubernetes with TensorFlow Serving Mar 23
- Kubernetes 1.2: Even more performance upgrades, plus easier application deployment and management Mar 17
- Kubernetes in the Enterprise with Fujitsu’s Cloud Load Control Mar 11
- ElasticBox introduces ElasticKube to help manage Kubernetes within the enterprise Mar 11
- State of the Container World, February 2016 Mar 1
- Kubernetes Community Meeting Notes - 20160225 Mar 1
- KubeCon EU 2016: Kubernetes Community in London Feb 24
- Kubernetes Community Meeting Notes - 20160218 Feb 23
- Kubernetes Community Meeting Notes - 20160211 Feb 16
- ShareThis: Kubernetes In Production Feb 11
- Kubernetes Community Meeting Notes - 20160204 Feb 9
- Kubernetes Community Meeting Notes - 20160128 Feb 2
- State of the Container World, January 2016 Feb 1
- Kubernetes Community Meeting Notes - 20160121 Jan 28
- Kubernetes Community Meeting Notes - 20160114 Jan 28
- Why Kubernetes doesn’t use libnetwork Jan 14
- Simple leader election with Kubernetes and Docker Jan 11
- Creating a Raspberry Pi cluster running Kubernetes, the installation (Part 2) Dec 22
- Managing Kubernetes Pods, Services and Replication Controllers with Puppet Dec 17
- How Weave built a multi-deployment solution for Scope using Kubernetes Dec 12
- Creating a Raspberry Pi cluster running Kubernetes, the shopping list (Part 1) Nov 25
- Monitoring Kubernetes with Sysdig Nov 19
- One million requests per second: Dependable and dynamic distributed systems at scale Nov 11
- Kubernetes 1.1 Performance upgrades, improved tooling and a growing community Nov 9
- Kubernetes as Foundation for Cloud Native PaaS Nov 3
- Some things you didn’t know about kubectl Oct 28
- Kubernetes Performance Measurements and Roadmap Sep 10
- Using Kubernetes Namespaces to Manage Environments Aug 28
- Weekly Kubernetes Community Hangout Notes - July 31 2015 Aug 4
- The Growing Kubernetes Ecosystem Jul 24
- Weekly Kubernetes Community Hangout Notes - July 17 2015 Jul 23
- Strong, Simple SSL for Kubernetes Services Jul 14
- Weekly Kubernetes Community Hangout Notes - July 10 2015 Jul 13
- Announcing the First Kubernetes Enterprise Training Course Jul 8
- Kubernetes 1.0 Launch Event at OSCON Jul 2
- How did the Quake demo from DockerCon Work? Jul 2
- The Distributed System ToolKit: Patterns for Composite Containers Jun 29
- Slides: Cluster Management with Kubernetes, talk given at the University of Edinburgh Jun 26
- Cluster Level Logging with Kubernetes Jun 11
- Weekly Kubernetes Community Hangout Notes - May 22 2015 Jun 2
- Kubernetes on OpenStack May 19
- Weekly Kubernetes Community Hangout Notes - May 15 2015 May 18
- Docker and Kubernetes and AppC May 18
- Kubernetes Release: 0.17.0 May 15
- Resource Usage Monitoring in Kubernetes May 12
- Weekly Kubernetes Community Hangout Notes - May 1 2015 May 11
- Kubernetes Release: 0.16.0 May 11
- AppC Support for Kubernetes through RKT May 4
- Weekly Kubernetes Community Hangout Notes - April 24 2015 Apr 30
- Borg: The Predecessor to Kubernetes Apr 23
- Kubernetes and the Mesosphere DCOS Apr 22
- Weekly Kubernetes Community Hangout Notes - April 17 2015 Apr 17
- Kubernetes Release: 0.15.0 Apr 16
- Introducing Kubernetes API Version v1beta3 Apr 16
- Weekly Kubernetes Community Hangout Notes - April 10 2015 Apr 11
- Faster than a speeding Latte Apr 6
- Weekly Kubernetes Community Hangout Notes - April 3 2015 Apr 4
- Paricipate in a Kubernetes User Experience Study Mar 31
- Weekly Kubernetes Community Hangout Notes - March 27 2015 Mar 28
- Kubernetes Gathering Videos Mar 23
- Welcome to the Kubernetes Blog! Mar 20