FAQ

What is replicaset

A ReplicaSet is a process that runs multiple instances of a Pod and keeps the specified number of Pods constant. Its purpose is to maintain the specified number of Pod instances running in a cluster at any given time to prevent users from losing access to their application when a Pod fails or is inaccessible.

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What is ReplicaSet in MongoDB?

A replica set in MongoDB is a group of mongod processes that maintain the same data set. Replica sets provide redundancy and high availability, and are the basis for all production deployments. This section introduces replication in MongoDB as well as the components and architecture of replica sets.

What is the difference between ReplicaSet and replication controller?

The replica set are also known as next generation replication controller. The only difference between replica set and replication controller is the selector types. The replication controller supports equality based selectors whereas the replica set supports equality based as well as set based selectors.

What is the difference between Deployment and replica set?

A ReplicaSet ensures that a specified number of pod replicas are running at any given time. However, Deployment is a higher-level concept that manages ReplicaSets and provides declarative updates to Pods along with a lot of other useful features.

How do I edit a ReplicaSet?

You can easily change the number of pods a particular ReplicaSet manages in one of two ways:

  1. Edit the controller’s configuration by using kubectl edit rs ReplicaSet_name and changing the replicas count up or down as you desire.
  2. Use kubectl directly. For example, kubectl scale –replicas=2 rs/web .

Is sharding better than replication?

What is the difference between replication and sharding? Replication: The primary server node copies data onto secondary server nodes. This can help increase data availability and act as a backup, in case if the primary server fails. Sharding: Handles horizontal scaling across servers using a shard key.

What is replica set in Kubernetes?

A ReplicaSet is one of the Kubernetes controllers that makes sure we have a specified number of pod replicas running. (Remember, a controller in Kubernetes is what takes care of tasks to make sure the desired state of the cluster matches the observed state.)

What is the use of Repllication controller?

A ReplicationController ensures that a specified number of pod replicas are running at any one time. In other words, a ReplicationController makes sure that a pod or a homogeneous set of pods is always up and available.

Why would you use a StatefulSet over a deployment or a ReplicaSet?

Use ‘StatefulSet’ with Stateful Distributed Applications, that require each node to have a persistent state. StatefulSet provides the ability to configure an arbitrary number of nodes, for a stateful application/component, through a configuration (replicas = N).

What is StatefulSet?

StatefulSets represent a set of Pods with unique, persistent identities and stable hostnames that GKE maintains regardless of where they are scheduled. The state information and other resilient data for any given StatefulSet Pod is maintained in persistent disk storage associated with the StatefulSet.

Is a deployment a ReplicaSet?

A ReplicaSet ensures that a specified number of pod replicas are running at any given time. However, a Deployment is a higher-level concept that manages ReplicaSets and provides declarative updates to Pods along with a lot of other useful features.

What are the possible states of Pod replica?

There are three possible container states: Waiting , Running , and Terminated . To check the state of a Pod’s containers, you can use kubectl describe pod <name-of-pod> .

When you define a ReplicaSet with one instance of a certain pod What happens when the pod dies?

A Replica Set allows you to define the number of pods that need to be running at all times and this number could be “1”. If a pod crashes, it will be recreated to get back to the desired state.

What is the difference between StatefulSet and Deployment?

Deployments are used for stateless applications, StatefulSets for stateful applications. The pods in a deployment are interchangeable, whereas the pods in a StatefulSet are not. Deployments require a service to enable interaction with pods, while a headless service handles the pods’ network ID in StatefulSets.

What is a Kubernetes StatefulSet?

StatefulSet is the workload API object used to manage stateful applications. Manages the deployment and scaling of a set of Pods, and provides guarantees about the ordering and uniqueness of these Pods. Like a Deployment, a StatefulSet manages Pods that are based on an identical container spec.

What is replica set in Openshift?

A replica set is a core Kubernetes object called ReplicaSet. A label query over a set of resources. The result of matchLabels and matchExpressions are logically conjoined. Equality-based selector to specify resources with labels that match the selector.

What is the main purpose of the mongos process?

Mongod = The primary daemon process for the MongoDB system. It handles data requests, manages data access, and performs background management operations. Show activity on this post.

What is MongoDB used for?

MongoDB is a document database used to build highly available and scalable internet applications. With its flexible schema approach, it’s popular with development teams using agile methodologies.

What is NoSQL language?

NoSQL, also referred to as “not only SQL”, “non-SQL”, is an approach to database design that enables the storage and querying of data outside the traditional structures found in relational databases.

What is difference between deployment and pod?

As we now know, a pod is the smallest unit of Kubernetes used to house one or more containers and run applications in a cluster, while deployment is a tool that manages the performance of a pod.

What is Kubernetes pod?

Pods are the smallest, most basic deployable objects in Kubernetes. A Pod represents a single instance of a running process in your cluster. Pods contain one or more containers, such as Docker containers. When a Pod runs multiple containers, the containers are managed as a single entity and share the Pod’s resources.

What is helm in Kubernetes?

What is Helm? In simple terms, Helm is a package manager for Kubernetes. Helm is the K8s equivalent of yum or apt. Helm deploys charts, which you can think of as a packaged application. It is a collection of all your versioned, pre-configured application resources which can be deployed as one unit.

What are operators Kubernetes?

In Kubernetes, an operator is an application-specific controller that can help you package, deploy, and manage a Kubernetes application. Ordinarily, you run and manage Kubernetes applications via the Kubernetes application programming interface (API) and kubectl tooling.

Who developed Kubernetes?

Google

Kubernetes was originally developed and designed by engineers at Google. Google was one of the early contributors to Linux container technology and has talked publicly about how everything at Google runs in containers.

What is deployment in Kubernetes?

A Kubernetes Deployment is used to tell Kubernetes how to create or modify instances of the pods that hold a containerized application. Deployments can scale the number of replica pods, enable rollout of updated code in a controlled manner, or roll back to an earlier deployment version if necessary.

What is the difference between DaemonSet and ReplicaSet?

In this way, ReplicaSet ensures that the number of pods of an application is running on the correct scale as specified in the conf file. Whereas in the case of DaemonSet it will ensure that one copy of pod defined in our configuration will always be available on every worker node.

What is StatefulSet and stateless in Kubernetes?

Kubernetes is well-known for managing stateless services. As far as deployment is concerned, pods are interchangeable. While a StatefulSet keeps a unique identity for each pod it manages. It uses the same identity whenever it needs to reschedule those pods.

What is Openshift StatefulSet?

StatefulSet represents a set of pods with consistent identities. Identities are defined as: Network: A single stable DNS and hostname. Storage: As many VolumeClaims as requested. The StatefulSet guarantees that a given network identity will always map to the same storage identity.

What is stateful and stateless?

Stateful Protocol. Stateless Protocol does not require the server to retain the server information or session details. Stateful Protocol require server to save the status and session information. In Stateless Protocol, there is no tight dependency between server and client.

Should I use StatefulSet?

When to use StatefulSet A Redis pod that has access to a volume, but you want it to maintain access to the same volume even if it is redeployed or restarted. A Cassandra cluster and have each node maintain access to its data. A webapp that needs to communicate with its replicas using known predefined network …

What is volumeClaimTemplates?

volumeClaimTemplates is a list of claims that pods are allowed to reference. The StatefulSet controller is responsible for mapping network identities to claims in a way that maintains the identity of a pod. Every claim in this list must have at least one matching (by name) volumeMount in one container in the template.

What is replicas in deployment?

Each time a new Deployment is observed by the Deployment controller, a ReplicaSet is created to bring up the desired Pods. If the Deployment is updated, the existing ReplicaSet that controls Pods whose labels match .spec.selector but whose template does not match .spec.template are scaled down.

Is a replica the same as a pod?

Replica Sets (usually written as ReplicaSets , without a space) are another abstraction layer on top of Pods. ReplicaSets guarantee that there will be a specific number of identical Pods running at any given time. When using ReplicaSets, you get to enforce a minimum number of Pods for your application.

Which of the following can be used to create Configmaps?

You can use kubectl create configmap to create a ConfigMap from an individual file, or from multiple files. You can pass in the –from-file argument multiple times to create a ConfigMap from multiple data sources.

How do you start a pod?

You can start this Pod by running:

  1. kubectl apply -f myapp.yaml. The output is similar to this: pod/myapp-pod created. …
  2. kubectl get -f myapp.yaml. …
  3. kubectl describe -f myapp.yaml. …
  4. kubectl logs myapp-pod -c init-myservice # Inspect the first init container kubectl logs myapp-pod -c init-mydb # Inspect the second init container.

How do I delete all pods in a replica set?

Delete ReplicaSet + Pods This is a standard and straightforward approach if you want to delete the ReplicaSet as well as the pods together by using subcommand delete with new-replica-set replaced with the name of ReplicaSet you want to delete.

How many containers can you run in a pod?

Remember that every container in a pod runs on the same node, and you can’t independently stop or restart containers; usual best practice is to run one container in a pod, with additional containers only for things like an Istio network-proxy sidecar.

What does POD stand for in banking?

Payable on Death

A Payable on Death (POD) beneficiary is an individual, group of individuals, non-profit, company, organization or trust, other than the owner or co-owner, designated by the owner(s) of the account to receive the balance of funds when the last owner on the account passes away.

What does the Kubernetes horizontal pod Autoscaler do?

The Horizontal Pod Autoscaler changes the shape of your Kubernetes workload by automatically increasing or decreasing the number of Pods in response to the workload’s CPU or memory consumption, or in response to custom metrics reported from within Kubernetes or external metrics from sources outside of your cluster.

How do you autoscale in Kubernetes?

Setting Up Autoscaling on GCE

  1. Run & Expose PHP-Apache Server. To demonstrate autoscaling we will use a custom docker image based on php-apache server. …
  2. Starting Horizontal Pod Autoscaler. Now that the deployment is running, we will create a Horizontal Pod Autoscaler for it. …
  3. Raising the Load. …
  4. Stop Load.

What is Kubernetes StatefulSet medium?

StatefulSet(stable-GA in k8s v1. 9) is a Kubernetes resource used to manage stateful applications. It manages the deployment and scaling of a set of Pods, and provides guarantee about the ordering and uniqueness of these Pods.

What is difference between Daemonset and deployment?

A Daemonset will not run more than one replica per node. Another advantage of using a Daemonset is that, if you add a node to the cluster, then the Daemonset will automatically spawn a pod on that node, which a deployment will not do.

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