EP 42: Designing a chat utility

This week’s system design refresher:

• CI/CD in 5 minutes (Youtube video)

• Visa dispute and chargeback

• Deployment technique

• Designing a chat utility

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A dispute occurs when a cardholder disagrees with a service provider’s cost. A chargeback is a technique of reversing the cost. Typically, the 2 phrases are used interchangeably.

A dispute is costly: for each greenback in disputed transactions, an extra $1.50 is spent on charges and bills.

• Steps 1-3: The cardholder, Bob raises a dispute with the cardboard issuer. The issuing financial institution opinions particulars. In circumstances of professional disputes, the issuing financial institution submits a chargeback request to the cardboard community.

• Steps 4-6: The cardboard community sends the dispute to the buying financial institution. After reviewing the main points, the buying financial institution may ask the service provider to resolve the difficulty.

• Steps 7,8: The service provider has two choices: 
  1. Retailers can settle for chargebacks if they seem professional. 
  2. The service provider can characterize to the issuer the doc that helps the transaction.

• Steps Sept. 11: The buying financial institution opinions the proof and represents the transaction to the cardboard community, which forwards it to the issuer.

• Steps 12-14: The issuer opinions the representment. There are two choices:
  1. The issuer expenses the transaction again to the cardholder;
  2. The issuer submits the dispute to the cardboard community for arbitration.

• Step 15: The cardboard community guidelines primarily based on the proof and assigns the ultimate legal responsibility to both the cardholder or the service provider.

👉 Over to you: Dispute is dear. How can we cut back it and make the method extra streamlined?

The diagram beneath exhibits a number of frequent deployment methods.

Massive Bang Deployment
Massive Bang Deployment is kind of easy, the place we simply roll out a brand new model in a single go along with service downtime. Preparation is crucial for this technique. We roll again to the earlier model if the deployment fails.
💡 No downtime ❌
💡 Focused customers ❌

Rolling Deployment
Rolling Deployment applies phased deployment in contrast with huge bang deployment. The entire plant is upgraded one after the other over a time period.
💡 No downtime ✅
💡 Focused customers ❌

Blue-Inexperienced Deployment
In blue-green deployment, two environments are deployed in manufacturing concurrently. The QA group performs varied assessments on the inexperienced setting. As soon as the inexperienced setting passes the assessments, the load balancer switches customers to it.
💡 No downtime ✅
💡 Focused customers ❌

Canary Deployment
With canary deployment, solely a small portion of cases are upgraded with the brand new model, as soon as all of the assessments cross, a portion of customers are routed to canary cases.
💡 No downtime ✅
💡 Focused customers ❌

Function Toggle
With function toggle, A small portion of customers with a selected flag undergo the code of the brand new function, whereas different customers undergo regular code. This can be utilized together of different methods: both the brand new department of code is upgraded in a single go, or only some cases are upgraded with new code.
💡 No downtime ✅
💡 Focused customers ✅

👉 Over to you: Which deployment methods have you ever used?

The diagram beneath exhibits a design for a simplified 1-to-1 chat utility.

Person Login Circulation

• Step 1: Alice logs in to the chat utility and establishes an online socket reference to the server facet.

• Steps 2-4: The presence service receives Alice’s notification, updates her presence, and notifies Alice’s buddies about her presence.

Messaging Circulation

• Steps 1-2: Alice sends a chat message to Bob. The chat message is routed to Chat Service A.

• Steps 3-4: The chat message is distributed to the sequencing service, which generates a novel ID, and is endured within the message retailer.

• Step 5: The chat message is distributed to the message sync queue to sync to Bob’s chat service.

• Step 6: Earlier than forwarding the messaging, the message sync service checks Bob’s presence:
  a) If Bob is on-line, the chat message is distributed to speak service B.
  b) If Bob is offline, the message is distributed to the push server and pushed to Bob’s gadget.

• Steps 7-8: If Bob is on-line, the chat message is pushed to Bob by way of the online socket

👉 Over to you: The right way to sync the chat messages amongst Alice’s totally different gadgets?