Replica

Q: How deeply does Bootstrapping Microservices, Second Edition: With Docker, Kubernetes, GitHub Actions, and Terraform cover replica?

Explains load balancing, restart behavior, and Kubernetes configuration, while deferring performance scaling details to a separate treatment.

As explained in Bootstrapping Microservices, Second Edition: With Docker, Kubernetes, GitHub Actions, and Terraform

A replica is an additional running instance that duplicates the functionality of another service or component.

A replica is an additional running instance of a microservice or component. Multiple replicas provide redundancy: a load balancer distributes requests across instances, while Kubernetes restarts failed instances. section 11.1 section 11.4.4

Use replicas to:

Maintain service during intermittent failures by redirecting requests to surviving instances. section 11.4.4
Distribute a larger workload across multiple instances when a microservice becomes a performance bottleneck. section 12.3.3
Recover failed instances with Kubernetes while continuing to log and investigate failures. section 11.4.4

Set three gateway replicas

Update a Kubernetes Deployment so its replicas field is 3, then apply the YAML with kubectl apply. The gateway runs three redundant instances instead of one. section 11.4.4

Listing 11.2 Adding replicas to our gateway microservice

apiVersion: apps/v1
kind: Deployment
metadata:
  name: gateway
spec:
  replicas: 3     #1
  selector:
    matchLabels:
      app: gateway
  template:
    metadata:
      labels:
        app: gateway
    spec:
      --snip--

Inspect the Deployment YAML showing where the replica count is configured. section 11.4.4

How Bootstrapping Microservices, Second Edition: With Docker, Kubernetes, GitHub Actions, and Terraform covers it

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Also explained in

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Elasticsearch in Action, Second EditionA duplicate copy of a primary shard maintained on a different node for redundancy and read availability.
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Platform Engineering on KubernetesA replica is an additional running instance of a service or application component that provides redundancy and capacity.
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Apache Kafka in ActionA Kafka replica is a copy of a partition maintained on a broker for fault tolerance and high availability.
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Kubernetes in Action, Second EditionAn application instance is a running replica of an application managed by Kubernetes.
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ScyllaDB in ActionA replica is a copy of database data maintained on another node for availability, resilience, or read serving.
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Learn Docker in a Month of Lunches, Second EditionA replica is an independently running instance of a workload maintained to provide capacity or redundancy.
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Acing the Certified Kubernetes Administrator Exam, Second EditionA replica is an independently running copy of a pod or application instance that contributes to workload capacity and redundancy.
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Server-Side WebAssemblyA replica is an independently running copy of a component or service deployed to handle workload alongside other copies.
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LLMs in ProductionA replica is an additional running instance of a service or workload that provides capacity or redundancy.
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LatencyA replica is a server or other system member that maintains a copy of data or state replicated from a primary.
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Kafka for ArchitectsA replica is a copy of a Kafka partition's records maintained on a broker for redundancy and availability.

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Related concepts

horizontal scalingused by · Horizontal scaling is adjusting system capacity by adding or removing computing nodes or equivalent instances that share or distribute the workload.
replicationproduced by · Replication is the creation or maintenance of multiple copies of data, state, or functionality across separate locations or components.
uptimeproduces · Uptime is the duration or proportion of a specified period during which a system or service is operational and available to provide its intended function.
primary nodecontrasts with · A primary node is a designated authoritative or coordinating member of a distributed system, typically responsible for accepting operations or coordinating replicated state.
load balancerused by · A load balancer is a hardware or software component that distributes incoming network traffic or requests among multiple destinations, such as servers or service instances.
in-sync replicaincludes · An in-sync replica is a Kafka partition replica sufficiently caught up with its leader to remain eligible for failover.

This explainer was generated by Manning's knowledge graph from the text of Bootstrapping Microservices, Second Edition: With Docker, Kubernetes, GitHub Actions, and Terraform. The section links point to the parts of the book it draws on.