While ReplicaSets can be used independently, today they're mainly used by Deployments as a mechanism to orchestrate Pod creation, deletion and updates. It’s mainly used by Deployment as a mechanism to orchestrate pod creation, deletion and updates. However, if you just want to distribute a deployment among all nodes then you can use pod anti affinity in your pod manifest file. A Deployment's Status does not match with what the corresponding ReplicaSet/Pods are showing. ; Cloud Manager. You can expand a managed domain to have more than one replica set per Microsoft Entra tenant. Frequently, when deploying a specific pod-template, the deployment fails to create a successful replicaset and no instance is created. Overview. if you delete a Deployments / Services, etc. Although ReplicaSet 's main purpose is to maintain a stable set of replica Pods, it's not a kubernetes object that is commonly created, at least not explicitly. Kubernetes events are a resource type in Kubernetes that are automatically created when other resources have state changes, errors, or other messages that should be broadcast to the system. 27. You can define a deployment to create a ReplicaSet or to remove deployments and adopt all their resources with new deployments. spec. In Kubernetes, you do not create ReplicaSets directly. kubectl delete deploy inginx-deploy. When to use a ReplicaSet. kubernetes. 1. string. Khi triển khai một ứng dụng mới thông qua Deployment, nó sẽ tạo ra một ReplicaSet mới để quản lý các Pod mới được tạo ra. I am not going to explain this approach in details because the link I provided is quite. » Prerequisites. However, ReplicaSet is still useful in certain cases where you only need the basic features of managing. Share. Similar to a ReplicationController, a ReplicaSet is a native Kubernetes API object that ensures a specified number of pod replicas are running at any given time. StatefulSet (stable-GA in k8s v1. We will create a ReplicaSet to ensure there is always 3 instances of a nginx. The differences in this manifest are: # kubectl create -f replicaset. But the replicas attribute on the Deployment object is actually related to this object. to the left of the replica set name to display all mongod processes in the replica set. Kubernetes creates a new ReplicaSet each time after the new Deployment config is deployed and. $ kubectl apply -f deployment. The original node affinity specified at the . The Pods and ReplicaSets are replaced individually, allowing old and new versions to briefly coexist. t. StatefulSet is the workload API object used to manage stateful applications. You signed out in another tab or window. Cet objet est souvent utilisé pour garantir la disponibilité d'un certain nombre identique de Pods. This hostname can be a hostname, an FQDN, an IPv4 address, or an IPv6 address. To estimate cost for. 15, 2023, 3:18 p. Hot Network QuestionsBased on the configuration you deployed with, both the deployment. Replication controller is kinda imperative, but replica sets try to be as declarative as possible. g. yml shown below. Optional. 式的定义方法，在 Deployment 对象中描述一个期望的状态，Deployment 控制器就会按照一定的控制 速率把实际状态改成期望状态，通过定义一个 Deployment 控制器会创建一个新的. The Deployment object specifies the desired state of your Deployment, and the Deployment Controller drives the current state of the system towards the desired state. Deployments manage ReplicaSets, and they help create multiple deployment strategies by appropriately manipulating them to produce the desired effect. Why Deployment manages multiple ReplicaSets? The answer is Kubernetes wants to support rollback mechanism. 1. Puedes monitorizar el progreso de un Deployment usando el comando kubectl rollout status. Imperative way: (this will then diverge from what you have in your yaml-file) kubectl scale deployment mage-di --replicas=2. Use this procedure to deploy a new replica set managed by Cloud. kubectl create -f my-replica-set. Deployment menurunkan kapasitas ReplicaSet yang lebih lama. 你负责描述 Deployment 中的目标状态，而 Deployment 控制器（Controller） 以受控速率更改实际状态， 使其变为期望状态。 你可以定义 Deployment 以创建新的 ReplicaSet，或删除现有 Deployment， 并通过新的 Deployment 收养其资源。A ReplicaSet is responsible for creating and scaling Pods, and for ensuring that Pods that fail are replaced. is highlighted above. spec. apiVersion:. To start with the deployment of the new cluster, go to the deploy option in the top right corner. Note: You can use kubectl delete for both imperative commands and imperative object configuration. El Deployment está escalando su ReplicaSet más nuevo. replicas field. Under the hood, Deployment creates a ReplicaSet which in turn creates pods on our cluster. kubectl delete deployment $ {our-deployment-name} And this seems to delete the deployment called our-deployment-name fine. The Deployment helps move between different versions of applications in the above diagram by moving between different Replicaset versions. Under the hood, Deployment creates a ReplicaSet which in turn creates pods on our cluster. kubectl apply -f dp. then apply it to the cluster with: kubectl apply -f k8-deployment. Related content: read our guide to Kubernetes Persistent Volumes. Un ReplicaSet (ensemble de réplicas en français) a pour but de maintenir un ensemble stable de Pods à un moment donné. yml. create a deployment. It will create Deployment object in imperative way. 🕸️Simple Difference Between ReplicaSet and Deployment. 18 the kubectl run will no longer create deployments but pods. The ReplicaSet is responsible for making sure that the number of replicas specified are always running. What might be used instead is the imperative option of kubectl create deployment. It is generated by hashing the PodTemplate of the ReplicaSet and using the resulting hash as the label value that is added to the. To create a replica said execute the following command. In the MongoDB spec section, the type of deployment was defined as ReplicaSet with the desired number of replicas of 3. We can also roll out an app via a ReplicaSet but a deployment resource give us a declarative application update. When you revise a deployment, a ReplicaSet is created that. revisionHistoryLimit is an optional field that specifies the number of old ReplicaSets to retain to allow rollback. Deployment status, notice only 2 ready replicas:A new deployment has been created and the release was successfully deployed on our AKS cluster. This is different from vertical scaling, which for Kubernetes would. Whenever we create a new deployment, K8s triggers a Rollout. @HunzlaSheikh When you run kubectl delete -f render. From what I can tell in the documentation, a ReplicaSet is created when running a Deployment. ReplicaSet ReplicaSet 的目的是维护指定数量的 Pod，常用做保障指定数量 Pod 的可用性 Deployment Deployment 是一个用来管理 ReplicaSet 的更高级概念，某种程度上我们不应该操作 ReplicaSet，而是直接使用 Deployment。Deployment 拥有 Rollout & Rollback 功能，方便我们管理。 StatefulSet StatefulSet 用来管理有状态的应用，其会. This means that a Deployment can have as many active ReplicaSets as possible, and eventually the deployment controller will scale down all old ReplicaSets and scale up the newest one. ReplicaSet is the next-generation ReplicationController that supports the new set-based label selector. A replica set, also known as a cluster, provides redundancy and availability. Pod baru menjadi siap atau dapat diakses (siap selama setidaknya MinReadySeconds). After it's paused you can make necessary changes to your configuration and then resume it by using kubectl rollout resume deployment/YOUR_DEPLOYMENT. ReplicaSet: StatefulSet is also a Controller but unlike Deployments, it doesn’t create ReplicaSet rather itself creates the Pod with a unique naming convention. For example, if you look at the above Deployment closely, you will see that it first creates a new Pod, then deletes an old Pod, and creates. While ReplicaSets can be used independently, today they're mainly used by Deployments as a mechanism to orchestrate Pod creation, deletion and updates. Rolling Deployment. x ReplicaSet. Deployment is a higher-level concept that manages ReplicaSets and provides declarative updates to Pods. The number of pods that have labels matching the labels of the pod template of the replicaset. 1 Answer. A replica set is a core Kubernetes object called ReplicaSet. added in kubernetes. StatefulSets. Two important columns of this output are: DESIRED displays the desired number of replicas of the application, which you define when you. Declarative way, edit this line in your Yaml file: replicas: 2. A. 1. A Replicaset is a K8s object, a set of Pod templates that describe a set of Pod replicas. Canary Deployments. Convert a Standalone mongod to a Replica Set. Update the deployment. If you check ReplicaSet after deploying a Deployment you will notice a ReplicaSet of the same name at the Deployment. spec. Under the hood, Deployment creates a ReplicaSet which in turn creates pods on our cluster. If you already have one or more database deployments, click Create. The trailing ReplicaSets that you can see after deployment deletion depends of the Revision History Limit that you have in your Deployment. The Deployment knows that the two Pods can't coexist in the same ReplicaSet, so it creates a second ReplicaSet to hold version 2. The Deployment creates a ReplicaSet that creates three replicated Pods, indicated by the . It's mainly used by Deployment as a mechanism to orchestrate pod creation, deletion and updates. StatefulSet と PVC の関係まとめ. Within the Deployment spec, there is always a ReplicaSet created. Actually, you will notice that the only change between declaring a Deployment and a ReplicaSet is the kind Note: A Deployment that configures a ReplicaSet is now the recommended way to set up replication. Deployments configure apps in a generic way. This manifest will define the desired state of the ReplicaSet, including the pod template for your application. When you updated the Deployment, it created a new ReplicaSet (nginx-deployment-1564180365) and scaled it up to 1 and waited for it to come up. When a Deployment is changed, the previous ReplicaSet needs to. In Kubernetes, a HorizontalPodAutoscaler automatically updates a workload resource (such as a Deployment or StatefulSet), with the aim of automatically scaling the workload to match demand. It is declarative and can be used for rolling updates of micro. It also needs to check whether the target pod is already managed by another controller (like a Deployment or another ReplicaSet). Imperative config management with commands. Create a new OpenShift Container Platform project. After you destroy the ReplicaSet, the running Pods will also get deleted. For all intents and purposes just use Deployments now. there is a deployment tool like ArgoCD / FluxCD / other tool that recreates them. Và nhiệm vụ của ReplicaSet là luôn đảm bảo số lượng Pod (current) sẽ luôn là 10 (bằng với DESIRED). The kubectl set env command updates the environment variables for a Kubernetes resource, such as a Deployment, ReplicaSet, or StatefulSet. The selectorfield under specdefines how this ReplicaSet identifies the pods it needs to manage. A ReplicaSet provides basic scaling mechanisms for pods, such as creating new pods if. 1- Vanilla Manifests. A ReplicationController ensures that a specified number of pod replicas are running at any one time. It ensures that the desired number of replicas (PODs with the application running), as mentioned while creating the Replicaset, is always maintained. This page shows how to run an application using a Kubernetes Deployment object. Use the kubectl apply command to create the ReplicaSet by applying the manifest:DaemonSet is a controller similar to ReplicaSet that ensures that the pod runs on all the nodes of the cluster. As per the name, ReplicaSet is used for managing the replicas. It uses a template to describe what each Pod must contain. When you see Replica Controller is mentioned in one the docs or other tutorials - refer to it as ReplicaSet AND consider using Deployment instead. Create a Deployment to rollout a ReplicaSet. A Pod is connected to a Daemon-/Replicaset or a Deployment by matching on its selectors. Next, create a release and a deployment for this project. Deployment is recommended for application services. To add an option: Click Add Advanced Options. In your scenario, the replicaset currently uses Selector app=nginx-app,pod-template-hash=b8b875889. ReplicaSet. selector field defines how the created ReplicaSet finds which Pods to manage. Create a file called. Now we have created a deployment and need to verify if the Nginx web servers were deployed correctly. Once the MongoDB resource is created, the operator will deploy a new. The deployment file contains details for a ReplicaSet that includes a PodTemplate. Now we’ll create a Kubernetes service using our deployment from the previous section. Below is the yaml file for Deployment. A ReplicaSet (RS) is a Kubernetes object used to maintain a stable set of replicated pods running within a cluster at any given time. Completar un. vi d. delete a Deployment to delete this replicaset. By default, it ensures that at most 125% of the desired number of Pods are up (25% max surge). You can define a deployment to create a ReplicaSet or to remove deployments and adopt all their resources with new deployments. You would have those many replicas running. spec. Identifying specific replica in kubernetes deployment programmatically. It’s possible to set more complex rules for pod selection, but. In mongosh, use rs. Concepts: Pod: A Pod is a group of one. For Deployment, ReplicaSet, Replication Controller, only scale, if the number of existing replicas matches. This document provides strategies for replica set deployments and describes common architectures. Kubernetes marks a Deployment as progressing when one of the following tasks is performed: The Deployment creates a new ReplicaSet. spec. So, if you want to change anything in the pod Spec, you should make that change in the deployment, not in the replicaset or the pod directly as they will get overwritten. yml deployment. Deployment – A Deployment is the most common way to get your app on Kubernetes. A standalone instance isn't a good choice for a production deployment because it can be a single point of failure. A deployment is a higher-level object that provides advanced features such as rolling updates, rollbacks, and self-healing capabilities, while a replicaset is a lower-level object that is. . In the case of a Job, this option is ignored. Additional replica sets in different Azure regions provide geographical disaster recovery for. selector field defines how the created ReplicaSet finds which Pods to manage. The Deployment can then manage the cleanup of older unused ReplicaSet s. For your convenience, I'm providing the example here as well. 14, 2023 Updated Nov. OwnerReferences[0]. You will almost never create this directly. Create a Service. Vì vậy, ta nên sử dụng Deployment Container thay vì sử dụng trực tiếp ReplicaSet trừ khi ta có nhu cầu đặc biệt cần phối hợp. What is a ReplicaSet?. This is where you specify how the ReplicaSet should. This is where PDB s provide the added advantage over the Replicaset. updating the image:, it will manage the creation of a new ReplicaSet for you. Important. OpenShift Container Platform adds expanded support for the software development and deployment lifecycle with the concept of deployments. Let's use the official example of a Deployment that creates a ReplicaSet to bring up three nginx Pods:If you deploy a pod from deployment object, kind:Deployment, then the deployment controller appends a unique name to pod that is part of specific deployment. This old ReplicaSet tries to spin up a pod and it stays in pending because of the resource limitations on the node. Changes to label selectors make existing pods fall out of ReplicaSet's scope, so if you change labels and label selector the pods are no longer "controlled" by ReplicaSet. There are many private registries in use. リソース 役割; Deployment: ReplicaSetを生成、管理しローリングアップデートやロールバックといったデプロイ管理を行います。: ReplicaSet: 同じ仕様のPodのレプリカ数を管理します。ReplicationControllerの後継に当たるものです。: Pod: アプリケーションを動かすための最小単位。To make changes in your current deployment you can use kubectl rollout pause deployment/YOUR_DEPLOYMENT. Deployments. When you create a ReplicaSet, you are essentially telling Kubernetes that you want a specific pod replicated x amount of times. The replica set name is immutable once deployed. Deployments ensure that by creating a ReplicaSet. If there are too many pods, it will kill some. A deployment creates a ReplicaSet that has the purpose of maintaining a "set" of "replicas" of said deployment. How does a deployment work? Behind the curtains, when you create a new deployment, K8s creates two different objects: a Pod definition, using as its specification what is available in the “template” field of the Deployment, and a ReplicaSet. In the simplest case, a deployment just creates a new replication. The situation is analogous to having a manager order "We need three workers doing this task at all times. The ReplicaSet ensures that the desired number of replicas (copies) are running at all times by creating or deleting Pods as needed. Create a Deployment to rollout a ReplicaSet. kubectl scale deployment <deployment-name> --replicas=3 My. Set any advanced configuration options for your MongoDB replica set. A Deployment creates Replicaset. But what ends up happening is all the pods in the replicaset inside the deployment will end up using the same shared volume and end up modifying the same data on disk. I found a guide that uses vanilla manifests for MongoDB deployment. The . ownerReferences" field with the ID of that ReplicaSet. Let’s now do a scale out test, where we will scale the deployment to 3. Understanding Deployment s. Patch your deployment either by running and edit the environment field there: kubectl edit. trafficSplitMethod - Traffic split method string. The following deployment strategies are supported in the built-in Kubernetes deployment object. You can monitor the progress for a Deployment by using kubectl rollout status. You can define a deployment to create a ReplicaSet or to remove deployments and adopt all their resources with new deployments. A pod is the smallest unit of deployment in Kubernetes, consisting of one or more containers that share resources and networks. By using a Deployment to manage a ReplicaSet, you can easily rollback to an earlier Deployment revision. The Scheduler, that is in charge of the pod resource allocation, commnd the kubelet, which reside on every worker nodes,. If you use Deployments to manage your Kubernetes workloads, and most people do, then they will leave behind one ReplicaSet for each change you make. Behind a deployment. By default, 10 old ReplicaSets will be kept, however its ideal value depends on the frequency and stability of new Deployments. 8. It seems to support some of the same features of a ReplicationController - scale up/down and auto restart, but it's not clear if it supports rolling upgrades or autoscale. apps values should count 2 available instances. . The ReplicaSet creates Pods in the background. As mentioned in the previous section, there are two ways to define or configure a ReplicaSet; directly through a YAML configuration file or through a deployment. When a new version of an application is deployed, the Deployment creates a new ReplicaSet with. 4 or later. 46. Replica Count: The number of replicas (pods) the controller should always be. Like deployment replicaset cant rollout or rollback to different version of application nor maintain any revisions for the same. Before you begin You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to. Now we’ll create a Kubernetes service using our deployment from the previous section. However, more sophisticated selection rules are possible, as. More information Before you. Always use a replica set in production. Now copy your deployment file to a master node and apply it. The Kubernetes docs explicitly suggest using a deployment rather than a ReplicaSet directly. core 2. Use this procedure to deploy a new replica set that Ops Manager. schedulerName field of the DaemonSet. I have a command to scale all the deployments to zero. Declare the new state of the Pods by changing the PodTemplateSpec of the deployment. In general, you can set up replica sets for testing either with RBAC enabled or disabled. The Deployment knows that the two Pods can't coexist in the same ReplicaSet, so it creates a second ReplicaSet to hold version 2. e. This procedure allows you to set different settings for the replica set resource, such as overrides for statefulSet configuration. You can scale down to 3 by running the command below. You may test it, after deleting the ReplicaSet and then typing the command kubectl get pods into the terminal. Note that there are no volumes or mounts. The following Deployment definition deploys four pods with nginx as their hosted application:Select the feature compatibility set . When both configured some unexpected behaviour might arise. 🔹 Pod: A pod is the smallest deployable unit in Kubernetes, representing a single instance of a running process. Regarding Endpoints and Namespace Controllers. However, more sophisticated selection rules are possible, as. The pod-template-hash label is added by the Deployment controller to every ReplicaSet that a Deployment creates or adopts. See moreDeployment resources enable declarative updates of Pods and ReplicaSets. // +optional CollisionCount *int32 `json:"collisionCount,omitempty" protobuf:"varint,8,opt,name=collisionCount"` }It seems a deployment has gotten stuck. The configuration of each Deployment revision is stored in its ReplicaSets; therefore, once an old ReplicaSet is deleted, you lose the ability to rollback to that revision of Deployment. What is a Kubernetes ReplicaSet? A ReplicaSet (RS) is a Kubernetes object used to maintain a stable set of replicated pods running within a cluster at any given time. It is a Kubernetes controller that matches the current state of your cluster to the desired state mentioned in the Deployment manifest. Ta thấy kết quả trả về có 1 ReplicaSet có tên là myapp-deployment-549fd4bf6c. You would have those many replicas running. Use this procedure to create a new replica set in a member Kubernetes cluster in a multi-Kubernetes-cluster deployment. Kubernetes - Deployment/replicaSet. kubectl apply -f dp. The Deployment controller uses this // field as a collision avoidance mechanism when it needs to create the name for the // newest ReplicaSet. 3. Và nhiệm vụ của ReplicaSet là. Cet objet est souvent utilisé pour garantir la disponibilité d'un certain nombre identique de Pods. I tried to update the Deployment and only the new ReplicaSet is updated. A Kubernetes pod is a cluster deployment unit that typically contains one or more containers. 롤링업데이트, 배포 중단, 롤백이 가능합니다. As such, it is often used to guarantee the availability of a specified. Summary. In Kubernetes, the Deployment resource is a declarative approach for managing the Pod and ReplicaSet resources. metadata: annotations: deployment. Deployment provides you the capabilities to upgrade your applications smoothly using rolling updates, undo changes, pause, and resume changes as required. apps/kuard created $ kubectl get deployment,replicaset,pod --show-labels NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE LABELS deployment. Replica Set is the next generation of Replication Controller. This will tell you what "owns" the pod. Convert a Standalone mongod to a Replica Set. of pods are matching the specified no. The difference between a ReplicaSet and a ReplicationController is that a ReplicaSet supports set-based selector requirements whereas a replication controller only supports equality. The . Replicaset will only ensure that the replicas number of pods will be created on other nodes during the process. nodeAffinity field (if specified) is taken into consideration by the DaemonSet controller when evaluating the eligible nodes, but is. Create a DaemonSet. In the case of a Job, this option is ignored. Deployment is a supervisor for pods. Replica Count: The number of replicas (pods) the controller should. Deployments create a new replica set whenever you do an update to the deployment. yaml, this will instruct Kubernetes to scale the current number of Pods to the value of. Then, the Deployment controller constantly works and monitors to ensure the actual state is as expected. Specify the full path of the directory where the. This is how the deployment controller looks up all the relevant pods of respective deployment. A ReplicaSet is a set of identical backup Pods maintained on the backend side to ensure a Pod is always available. Let's understand the differences between Deployment, ReplicaSet, and Pod. A replica set, also known as a cluster, provides redundancy and availability. If you just have a Replicaset with one replica and no PodDisruptionBudget specified, the pod will be terminated and a new pod will be created on other nodes. tier=backend. A ReplicaSet, as the name implies, is a set of replicas (Pods) maintained with their Revision history. Il a ensuite poursuivi la montée en puissance du. When this ReplicaSet is created it will start the desired number of Pods from the template. Ta thấy kết quả trả về có 1 ReplicaSet có tên là myapp-deployment-549fd4bf6c. a ReplicaSet is a native Kubernetes API object that ensures a specified number of pod replicas are. Currently, it is being maintained by the cloud native computing foundation (CNCF). ReplicaSet is the next-generation ReplicationController that. Alternatives to ReplicaSet Deployment (recommended) Deployment is an object which can own ReplicaSets and update them and their Pods via declarative, server-side rolling updates. A ReplicaSet’s purpose is to run a specified number of pods at any given time. Deployment is an abstraction over ReplicaSet. Deployment resources enable declarative updates of Pods and ReplicaSets. kubectl get replicaset. If you see the logs, they are starting from 73, meaning that the previous pod had written till 72 in the file and. kubectl label nodes <node> <key>=<value>. Sometimes, Kubernetes sets the value of ownerReference automatically. selector field defines how the created ReplicaSet finds which Pods to manage. While ReplicaSets can be used independently, today they're mainly used by Deployments as a mechanism to orchestrate Pod creation, deletion and updates. The old one remains the same. Update the replica set configuration when the hostname of a member's corresponding mongod. Sorted by: 6. Now copy your deployment file to a master node and apply it. Also, the template used to create the Pods will be specified in the Deployment YAML file. Complete Deployment. Clean up Policy. It gives us fine-grained control over how and when a new pod version is rolled out. Deployment Guidelines. revisionHistoryLimit is an optional field that specifies the number of old ReplicaSets to retain to allow rollback. The ReplicaSet creates Pods in the background. Alternatives to ReplicaSet Deployment (recommended) Deployment is an object which can own ReplicaSets and update them and their Pods via declarative, server-side rolling updates. A Deployment is another layer above ReplicaSets and Pods, newer and more advanced level concept than ReplicaSets. I have written a bash script to get all deployments on a kubernetes cluster. If you see the logs, they are starting from 73, meaning that the previous pod had written till 72 in the file and. Labels are used to enrich resources with metadata often describing things like the resource's purpose, environment, and version. The United States and China, the world’s two largest climate polluters, have agreed to jointly tackle. Share. A ReplicaSet ensures that a specified number of Pod replicas are running continuously and helps with load-balancing in case of an increase in resource usage. The Deployment creates a ReplicaSet that creates three replicated Pods, indicated by the . StatefulSetsA Replicaset is a structure that enables you to easily create multiple pods, then make sure that that number of pods always exists. Normally, the old (previous). Un ReplicaSet (ensemble de réplicas en français) a pour but de maintenir un ensemble stable de Pods à un moment donné. yaml file of helm) to any number. However, more sophisticated selection rules are possible, as. For Deployment, ReplicaSet, Replication Controller, only scale, if the number of existing replicas matches. 📍 Deployment vs ReplicaSet vs Pod: In Kubernetes, different objects serve various purposes when managing pods. Kind you can write code to find the Pod manager/controller depending on the type (ReplicaSet, DaemonSet, etc). Deployment is the easiest and most used resource for deploying your application. Only the following resource creation is possible using kubectl create:. but the problem is i need to clean all old deployment and replica set once new version deployed successfully. In docs about owners and dependents it says:. , but they are recreated again. Create credentials for the Kubernetes Operator or configure a different secret storage tool. The relation between Deployment, Replicaset & POD. When you create a Deployment in Kubernetes, a ReplicaSet is created automatically. Add an arbiter to give a replica set an odd number of voting members to prevent election ties.