Don't Attend a Backend Interview Before Watching This Video

[00:00:00]Most back-end developers know how to build APIs and connect databases, but real back-end engineering begins when thousands of users start sending requests at the same time. Databases slow down, servers fail, messages get duplicated, and small mistakes become major outages.

[00:00:17]So, here are 10 back-end concepts every developer should know.

[00:00:22]Number one, HTTP and APIs.

[00:00:25]Back-ends usually communicate through HTTP. Get retrieves data, post creates data, put replaces data, patch updates part of it, delete removes it.

[00:00:39]The server then returns a status code, such as 200 for success, 400 for an invalid request, 401 for unauthenticated access, 403 for forbidden access, or 500 for a server error.

[00:00:54]Number two, authentication and authorization.

[00:00:58]Authentication answers, "Who are you?"

[00:01:01]Authorization answers, "What are you allowed to do?"

[00:01:04]Logging in proves your identity.

[00:01:07]Authorization decides whether you can view, edit, or delete something.

[00:01:11]A back-end should always verify permissions on the server.

[00:01:15]Number three, database indexes.

[00:01:18]Imagine searching for one user inside a table with millions of rows.

[00:01:23]Without an index, the database may scan the entire table.

[00:01:27]An index works like the index of a book.

[00:01:30]It helps the database find records faster.

[00:01:32]But, indexes also use storage and slow down rights, so only index columns that are frequently searched, joined, or sorted.

[00:01:41]Number four, transactions.

[00:01:44]A transaction groups multiple database operations into one action.

[00:01:48]During a bank transfer, money must be removed from one account and added to another.

[00:01:53]If one step fails, the entire transaction should be rolled back.

[00:01:58]Transactions protect data from becoming incomplete or inconsistent.

[00:02:03]Number five, concurrency and race conditions.

[00:02:07]Back ends process many requests at the same time.

[00:02:10]Imagine two users trying to buy the final concert ticket. Both requests may see that the ticket is available and both may complete the purchase. That is a race condition.

[00:02:21]Transactions, locks, unique constraints, and atomic operations can help prevent it.

[00:02:27]Number six, caching.

[00:02:30]Frequently requested data can be stored in a fast cache such as Redis.

[00:02:35]The back end checks the cache before querying the database.

[00:02:38]If the data exists, it is returned immediately.

[00:02:42]Caching improves performance and reduces database load.

[00:02:45]The main challenge is keeping cached data up-to-date.

[00:02:49]Number seven, message queues.

[00:02:52]Some tasks should run in the background.

[00:02:55]After an order is placed, the system may need to send an email, create an invoice, update inventory, and notify the warehouse.

[00:03:03]Instead of making the user wait, the back end can place these tasks into a queue.

[00:03:08]Workers then process them separately using tools such as Kafka, RabbitMQ, SQS, or Azure Service Bus.

[00:03:17]Number eight, item potency.

[00:03:19]An item potent operation can be repeated without creating an incorrect result.

[00:03:24]Imagine a payment succeeds, but the response is lost. The user retries the request.

[00:03:30]Without item potency, they could be charged twice.

[00:03:34]An item potency key allows the back end to recognize repeated requests and return the original result.

[00:03:41]Number nine, rate limiting.

[00:03:43]A back end cannot accept unlimited requests.

[00:03:46]Rate limiting controls how many requests a user or application can make within a certain period.

[00:03:52]For example, an API may allow 100 requests per minute.

[00:03:57]When the limit is reached, the server usually returns status code 429.

[00:04:02]This protects the system from abuse and overload.

[00:04:06]Number 10, scalability and load balancing.

[00:04:10]As traffic grows, you can scale vertically by using a more powerful server or scale horizontally by adding more servers.

[00:04:17]A load balancer distributes incoming requests across those servers and avoids unhealthy instances.

[00:04:24]Horizontal scaling works best when the back end is stateless, meaning any server can handle any request.

[00:04:31]And those are 10 back end concepts every developer should know.

[00:04:35]HTTP explains communication.

[00:04:38]Authentication protects identity.

[00:04:40]Indexes improve database performance.

[00:04:43]Transactions protect data.

[00:04:45]Concurrency prevents race conditions.

[00:04:48]Caching improves speed.

[00:04:50]Queues handle background work.

[00:04:53]Item potency prevents duplicates.

[00:04:55]Rate limiting protects the system.

[00:04:57]And load balancing helps it scale.

[00:05:00]Once you understand these concepts, you stop thinking only about writing code.

[00:05:05]You start thinking about performance, reliability, security, and system design.