Zero-downtime deployment concept in Express - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the main goal of zero-downtime deployment in Express apps?

Choose the best description of zero-downtime deployment for an Express server.

A To deploy new code only during scheduled maintenance windows with downtime.

B To restart the server immediately after deployment, causing a brief downtime.

C To update the server code without stopping the server or dropping user requests.

D To disable all incoming requests during deployment to avoid errors.

💡 Hint

Think about user experience during deployment.

Zero-downtime deployment means updating the server without interrupting active users or dropping requests. The server keeps running while new code is loaded.

❓ component_behavior

intermediate

How does a load balancer help achieve zero-downtime deployment?

Select the option that best explains the role of a load balancer in zero-downtime deployment.

A It distributes incoming requests between old and new server instances to avoid downtime.

B It restarts the server automatically after deployment.

C It blocks all traffic during deployment to prevent errors.

D It directs traffic only to the old server version until the new one is fully ready.

💡 Hint

Think about how traffic is managed between multiple servers.

A load balancer sends requests to both old and new server versions during deployment, so users experience no downtime.

❓ lifecycle

advanced

What is the correct sequence for zero-downtime deployment steps in Express?

Order the steps to perform a zero-downtime deployment correctly.

A 1,2,3,4

B 2,1,3,4

C 1,3,2,4

D 3,1,2,4

💡 Hint

Think about starting new first, then switching traffic, then stopping old.

The new server starts first, then the load balancer directs traffic to it. After that, the old server stops receiving traffic and finally shuts down.

🔧 Debug

advanced

Why does this zero-downtime deployment code cause downtime?

Identify the problem in this Express deployment snippet: const server = app.listen(3000); // Deploy new code server.close(); app.listen(3000); Options:

A The port 3000 is not freed immediately after server.close(), causing a bind error.

B Calling server.close() stops the server before the new one starts, causing downtime.

C The new app.listen(3000) call is missing a callback, causing errors.

D The app variable is not reinitialized with new code before listening.

💡 Hint

Think about when the server stops accepting requests.

Calling server.close() stops the server immediately, so there is downtime before the new server starts listening.

❓ state_output

expert

What is the output of this Express zero-downtime deployment simulation?

Given this simplified code simulating zero-downtime deployment, what is logged? let activeServers = 1; function deployNewVersion() { activeServers++; console.log(`Servers running: ${activeServers}`); activeServers--; console.log(`Servers running: ${activeServers}`); } deployNewVersion();

A

Servers running: 1
Servers running: 1

B

Servers running: 1
Servers running: 2

C

Servers running: 2
Servers running: 2

D

Servers running: 2
Servers running: 1

💡 Hint

Track the value of activeServers after each operation.

The function increments activeServers to 2, logs it, then decrements back to 1 and logs again.