{"id":26248,"date":"2022-01-10T10:41:38","date_gmt":"2022-01-10T10:41:38","guid":{"rendered":"https:\/\/www.devopsschool.com\/blog\/?p=26248"},"modified":"2022-03-04T12:52:36","modified_gmt":"2022-03-04T12:52:36","slug":"interview-questions-answers-complete-guide-for-consul","status":"publish","type":"post","link":"https:\/\/www.devopsschool.com\/blog\/interview-questions-answers-complete-guide-for-consul\/","title":{"rendered":"Interview Questions & Answers Complete Guide for Consul"},"content":{"rendered":"\n

What exactly is Consul?<\/strong>
Consul is an open-source platform for service networking developed by HashiCorp. Consul is a service mesh solution with a full-featured control plane for service discovery, configuration, and segmentation. Each of these features can be used separately or in tandem to create a complete service mesh. Consul requires the use of a data plane and provides a proxy as well as a native integration mechanism. Consul includes a built-in proxy that allows you to get started right away, but it also supports third-party proxy integrations such as Envoy.<\/p>\n\n\n\n

What are the key features of Consul?<\/strong><\/p>\n\n\n\n

Consul was designed with DevOps and application developers in mind, with a focus on modern, elastic infrastructures.<\/p>\n\n\n\n

Discovering Services- Clients of Consul can register a service, such as api or mysql, and other clients can use Consul to find providers. Using DNS or HTTP, applications can quickly locate the services they require.<\/p>\n\n\n\n

Examine your health- Consul clients keep track of cluster health and assist service discovery components in avoiding sending traffic to unhealthy hosts.<\/p>\n\n\n\n

KV Store- Dynamic configuration, feature flagging, coordination, and leader election are just a few of the applications for Consul’s hierarchical key\/value store.
Communication between services that is secure<\/p>\n\n\n\n

Secure Service Communication- Consul can generate and distribute TLS certificates for services in order to establish mutual TLS connections. Intentions can be used to specify which services are allowed to talk to each other. Service segmentation can be easily managed with intentions that can be changed in real time, rather than using complex network topologies and static firewall rules.<\/p>\n\n\n\n

Datacenters in multiple locations- Consul is capable of supporting multiple data centers. This means that users of Consul will not have to worry about adding more abstraction layers in order to expand to multiple locations.<\/p>\n\n\n\n

What is the purpose of Consul Architecture?<\/strong><\/p>\n\n\n\n

Consul, as can be seen, is in charge of three different servers. The Raft algorithm is used in the working architecture to select a leader from among the three servers. These servers are given names like Follower and Leader. As the name implies, the follower is responsible for adhering to the leader’s decisions. All three servers are linked together for any communication.<\/p>\n\n\n\n

Each server communicates with its own client using the RPC concept. Clients can communicate with one another using the Gossip Protocol. TCP or the gossip communication technique can be used to make the internet communication facility available. This communication is done directly with one of the three servers.<\/p>\n\n\n\n

In Consul, what is the Raft Algorithm?<\/strong><\/p>\n\n\n\n

Raft is a log management algorithm that uses a consensus algorithm to manage a replicated log. It’s based on the CAP Theorem, which states that when there’s a network partition, you have to choose between consistency and availability. Not all three fundamentals of the CAP Theorem can be met at any given time. For any two of them, at the very least, a tradeoff must be made.<\/p>\n\n\n\n

Multiple servers, usually in odd numbers, make up a Raft Cluster. For example, if we have five servers, the system can withstand two failures. At any given time, each server is in one of three states: Leader, Follower, or Candidate. There is only one leader in a typical operation, and every other server is a follower. These followers are in a passive state, which means they don’t make requests on their own but rather respond to those made by the candidate and the leaders.<\/p>\n\n\n\n

What Exactly Is A Checkpoint? \/ Does<\/strong> Consul Call Home?<\/strong><\/p>\n\n\n\n

Consul makes use of Checkpoint, a HashiCorp service that checks for updates and critical security bulletins. Checkpoint receives only anonymous data that cannot be used to identify the user or host. An anonymous ID is sent, which aids in the de-duplication of alert messages. This pseudonymous ID can be turned off. Using the Checkpoint service is, in fact, optional and can be turned off.<\/p>\n\n\n\n

Is Consul a UDP<\/strong> Broadcast Or Multicast System?<\/strong><\/p>\n\n\n\n

Consul employs the Serf gossip protocol, which is based on unicast TCP and UDP. In a multi-tenant or cloud network environment, broadcast and multicast are rarely available. As a result, both Consul and Serf were created to avoid any reliance on those abilities.<\/p>\n\n\n\n

Is Consul Eventually Consistent<\/strong> Or Consistently Consistent?<\/strong><\/p>\n\n\n\n

The service catalogue and the gossip protocol are two important subsystems of Consul. All nodes, service instances, health check data, ACLs, and KV information are stored in the service catalogue. It has a high level of consistency and has been replicated using the consensus protocol.<\/p>\n\n\n\n

The gossip protocol is used to keep track of which nodes are in the cluster as well as to detect node or agent failure. By its very nature, this data is eventually consistent. The service catalogue is updated when the servers detect a change in membership or receive a health update.<\/p>\n\n\n\n

The answer to the question is nuanced as a result of this split. Almost every client API interacts with the service catalogue and follows a strict set of rules. Updates to the catalogue may arrive via the gossip protocol, which is eventually consistent, so the catalog’s current state may lag until the state is reconciled.<\/p>\n\n\n\n

Is Delta<\/strong> Updates For<\/strong> Watchers Or Blocking Queries Supported By<\/strong> Consul?<\/strong>
A delta or a change-only response to a watcher or a blocking query is not currently supported by Consul. The API simply allows for a full-result edge-trigger return. A client should save the results of their most recent read and compute the delta on the client side.<\/p>\n\n\n\n

Instead of attempting to support the delta calculation, Consul offloads it to clients by design. This eliminates the need for costly server maintenance as well as race conditions between data updates and watch registrations.<\/p>\n\n\n\n

Consul uses which<\/strong> network ports?<\/strong><\/p>\n\n\n\n

Consul uses all of the ports listed in the Ports Used section of the Configuration documentation.<\/p>\n\n\n\n

Is\u00a0it\u00a0necessary\u00a0for\u00a0Consul\u00a0to\u00a0set\u00a0resource\u00a0limits\u00a0for\u00a0user\u00a0processes?<\/strong>
A\u00a0Consul\u00a0client\u00a0agent\u00a0should\u00a0only\u00a0require\u00a0a\u00a0small\u00a0number\u00a0of\u00a0open\u00a0file\u00a0descriptors.\u00a0Each\u00a0connection\u00a0to\u00a0the\u00a0client\u00a0agent\u00a0(for\u00a0example,\u00a0for\u00a0a\u00a0blocking\u00a0query)\u00a0will\u00a0open\u00a0a\u00a0connection,\u00a0and\u00a0there\u00a0will\u00a0typically\u00a0be\u00a0connections\u00a0to\u00a0one\u00a0of\u00a0the\u00a0Consul servers.\u00a0Watch\u00a0handlers,\u00a0health\u00a0checks,\u00a0log\u00a0files,\u00a0and\u00a0other\u00a0applications\u00a0require\u00a0a\u00a0small\u00a0number\u00a0of\u00a0file\u00a0descriptors.<\/p>\n\n\n\n

You should plan on the above requirements for a Consul server agent, as well as an additional incoming connection from each node in the cluster. Although this should not be the case in most cases, in the worst-case scenario, if one of the other servers fails, the other client agents should all connect to the same server, so planning for this possibility is beneficial.<\/p>\n\n\n\n

The default limits are usually sufficient for Consul, but before arbitrarily increasing the limits, you should carefully examine your own environment’s specific needs and identify the root cause of any excessive resource utilization.<\/p>\n\n\n\n

What is the size limit for per-key<\/strong> value sizes in Consul’s Key\/Value Store?<\/strong><\/p>\n\n\n\n

The maximum size of a key’s value is 512KB. This is strictly enforced, and any client attempting to store more than that limit in a value will receive an HTTP 413 response. It’s important to keep in mind that the Consul key\/value store isn’t intended to be used as a general-purpose database. For more information, see Server Performance.<\/p>\n\n\n\n

What Information Is Shared<\/strong> Among Consul Datacenters?<\/strong>
Data is not replicated between different Consul datacenters in general. When a request is made for a resource in another datacenter, the local Consul servers send an RPC request to that resource’s remote Consul servers and return the results. If the remote datacenter is unavailable, those resources will be unavailable as well, but the local datacenter will be unaffected. A limited subset of data can be replicated in some special cases, such as with Consul’s built-in ACL replication capability or external tools like consul-replicate.<\/p>\n\n\n\n

What Is<\/strong> A Consul Server And How Does It Work?<\/strong>
Consul is a service discovery and configuration system that is distributed, highly available, and datacenter-aware. It can be used to present services and nodes in a flexible and powerful interface that allows clients to have an always-up-to-date view of the infrastructure to which they belong.
What Is Hashicorp Consul and How Does It Work?<\/strong>
HashiCorp Consul is an open source tool that provides service discovery, health checks, load balancing, a service graph, mutual TLS identity enforcement, and a configuration key-value store to address these new complexities. Consul is an ideal control plane for a service mesh because of these features.<\/p>\n\n\n\n

What Is Docker Consul<\/strong> and How Does It Work?<\/strong>
We’re excited to announce the availability of our official Consul Docker image. Consul is a modern datacenter runtime that allows you to discover, configure, and orchestrate services. Consul is the first tool in the Consul family to have an official Docker image.<\/p>\n\n\n\n

What Exactly Is A Consul Agent?<\/strong><\/p>\n\n\n\n

Consul’s core process is the Consul agent. The agent is in charge of maintaining membership information, registering services, performing checks, and responding to queries, among other things. The agent must be installed on each node in a Consul cluster. Any agent can run in either client or server mode.<\/p>\n\n\n\n

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