Least connections in Nginx - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the load balancing method to least connections in NGINX.

Nginx

upstream backend {
    [1];
    server backend1.example.com;
    server backend2.example.com;
}

Drag options to blanks, or click blank then click option'

Aleast_conn

Bproxy_pass

Clisten

Dserver

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'proxy_pass' instead of 'least_conn' inside the upstream block.

Placing 'least_conn' outside the upstream block.

The least_conn directive sets the load balancing method in an upstream block. Using least_conn; tells NGINX to use the least connections method.

2fill in blank

medium

Complete the code to enable least connections load balancing with a parameter to control the maximum number of connections.

Nginx

upstream backend {
    least_conn [1];
    server backend1.example.com;
    server backend2.example.com;
}

Drag options to blanks, or click blank then click option'

Amax_conns=5

Bmax_fails=3

Cweight=2

Dfail_timeout=10s

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing max_fails with connection limits.

Using weight which is for weighted load balancing.

The max_conns parameter limits the maximum simultaneous connections to a server when using least connections load balancing.

3fill in blank

hard

Fix the error in the upstream block to correctly use least connections load balancing.

Nginx

upstream backend {
    [1];
    server backend1.example.com;
    server backend2.example.com;
}

Drag options to blanks, or click blank then click option'

Aproxy_pass

Blisten

Cleast_conn

Dserver

Attempts:

3 left

💡 Hint

Common Mistakes

Misspelling the 'least_conn' directive.

Using directives not valid inside upstream blocks.

The directive balanc is a typo. The correct directive is least_conn to set the load balancing method.

4fill in blank

hard

Fill both blanks to configure an upstream block using least connections with max connections limit and a server with weight.

Nginx

upstream backend {
    least_conn [1];
    server backend1.example.com [2];
}

Drag options to blanks, or click blank then click option'

Amax_conns=10

Bweight=3

Cmax_fails=2

Dfail_timeout=5s

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up max_fails and max_conns.

Placing weight outside the server directive.

Use max_conns=10 to limit connections and weight=3 to assign server weight.

5fill in blank

hard

Fill all three blanks to create an upstream block with least connections, max connections limit, and two servers with weights.

Nginx

upstream backend {
    least_conn [1];
    server backend1.example.com [2];
    server backend2.example.com [3];
}

Drag options to blanks, or click blank then click option'

Amax_conns=15

Bweight=4

Cweight=2

Dmax_fails=3

Attempts:

3 left

💡 Hint

Common Mistakes

Using max_fails instead of max_conns for connection limits.

Assigning weights outside server lines.

The max_conns=15 limits connections, and the servers have weights 4 and 2 respectively.

Practice

1. What does the least_conn directive do in an nginx upstream block?

easy

A. Sends new requests to the server with the fewest active connections

B. Sends new requests to the server with the fastest response time

C. Sends new requests to servers in a round-robin order

D. Sends new requests to the server with the most active connections

Solution

1. Step 1: Understand the purpose of least_conn

   The least_conn directive is used to balance load by sending requests to the server with the fewest active connections.

2. Step 2: Compare with other load balancing methods

   Other methods like round-robin or fastest response time differ; least_conn focuses on active connections count.

3. Final Answer:

   Sends new requests to the server with the fewest active connections -> Option A

4. Quick Check:

   Least connections = fewest active connections [OK]

Hint: Least connections means pick server with fewest active users [OK]

Common Mistakes:

• Confusing least connections with round-robin
• Thinking it picks fastest server instead
• Assuming it sends to server with most connections

2. Which of the following is the correct syntax to enable least connections load balancing in nginx?

easy

A. upstream backend { least_conn; server 192.168.1.1; }

B. upstream backend { least_connections; server 192.168.1.1; }

C. upstream backend { least_conn_load; server 192.168.1.1; }

D. upstream backend { leastconn; server 192.168.1.1; }

Solution

1. Step 1: Recall the exact directive name

   The correct directive to enable least connections is least_conn inside the upstream block.

2. Step 2: Verify syntax correctness

   Options A, B, and D use incorrect directive names or misspellings.

3. Final Answer:

   upstream backend { least_conn; server 192.168.1.1; } -> Option A

4. Quick Check:

   Correct directive = least_conn [OK]

Hint: Use exact directive name 'least_conn' inside upstream block [OK]

Common Mistakes:

• Using 'least_connections' instead of 'least_conn'
• Misspelling the directive as 'leastconn' or 'least_conn_load'
• Placing directive outside the upstream block

3. Given this nginx upstream configuration:
<pre>upstream backend { least_conn; server 10.0.0.1; server 10.0.0.2; } If 10.0.0.1 has 5 active connections and 10.0.0.2 has 3 active connections, where will the next request be sent?

medium

A. To 10.0.0.1 because it is listed first

B. To both servers equally

C. To 10.0.0.2 because it has fewer active connections

D. To 10.0.0.1 because it has more active connections

Solution

1. Step 1: Identify the load balancing method

   The least_conn method sends requests to the server with the fewest active connections.

2. Step 2: Compare active connections of servers

   10.0.0.1 has 5 connections, 10.0.0.2 has 3 connections, so the next request goes to 10.0.0.2.

3. Final Answer:

   To 10.0.0.2 because it has fewer active connections -> Option C

4. Quick Check:

   Least connections picks server with 3 connections [OK]

Hint: Pick server with smallest active connections count [OK]

Common Mistakes:

• Choosing server listed first instead of fewest connections
• Assuming equal distribution regardless of connections
• Picking server with more connections by mistake

4. You configured nginx with least_conn but all requests keep going to the same server. What is the most likely cause?

medium

A. The servers have equal active connections, so nginx picks the first server always

B. The least_conn directive is misspelled in the config

C. The upstream block is missing the server directives

D. The nginx service was not reloaded after configuration change

Solution

1. Step 1: Check if configuration changes are active

   If nginx is not reloaded after config changes, old settings remain active causing unexpected behavior.

2. Step 2: Consider other causes

   Misspelling or missing servers cause errors or no load balancing, but requests going to one server usually means config not applied.

3. Final Answer:

   The nginx service was not reloaded after configuration change -> Option D

4. Quick Check:

   Reload nginx after config changes [OK]

Hint: Always reload nginx after config edits to apply changes [OK]

Common Mistakes:

• Ignoring the need to reload nginx after config update
• Assuming equal connections cause all traffic to one server
• Not verifying server directives exist in upstream block

5. You have three backend servers with varying response times and active connections:

• Server A: 2 active connections, slow response
• Server B: 5 active connections, fast response
• Server C: 2 active connections, medium response

Using least_conn load balancing, which server will receive the next request and why?

hard

A. Requests will be evenly distributed among all servers

B. Server A, because it has the fewest active connections and slow response is ignored

C. Server C, because it has the fewest active connections and better response than A

D. Server B, because it has the fastest response time despite more connections

Solution

1. Step 1: Understand least_conn prioritizes active connections

   It sends requests to servers with the fewest active connections, ignoring response time.

2. Step 2: Compare servers with fewest connections

   Server A and C both have 2 connections, but least_conn does not consider response speed, so it picks the first with fewest connections, Server A.

3. Final Answer:

   Server A, because it has the fewest active connections and slow response is ignored -> Option B

4. Quick Check:

   Least connections ignores speed, picks fewest active connections [OK]

Hint: Least connections ignores speed; picks server with fewest active connections [OK]

Common Mistakes:

• Assuming fastest response server is chosen with least_conn
• Thinking least_conn balances by response time
• Expecting even distribution regardless of connections