C100DBA Server Administration Practice Test 2 — 15 Questions

Question 1

A DBA needs to add a new member to an existing replica set. The new member must be configured as a hidden member with a priority of 0 and a delay of 3600 seconds to serve as a delayed backup. Which sequence of commands should the DBA use?

Choose an answer to begin — your selection is scored in the full session.

Accepted Answer

rs.add({ host: 'newhost:27017', hidden: true, priority: 0, slaveDelay: 3600 }). The rs.add command can take a configuration document that includes hidden, priority, and slaveDelay. This single command adds the new member with all desired properties: hidden: true makes it hidden, priority: 0 prevents it from becoming primary, and slaveDelay: 3600 delays replication by one hour. Using rs.add with the full configuration is the correct and efficient method. Other options either use incorrect field names or require a risky multi-step reconfiguration. (Explanation length: 65 words)

Answer

rs.add({ host: 'newhost:27017', hidden: true, priority: 0, secondaryDelaySecs: 3600 })

Answer

rs.add({ host: 'newhost:27017', hidden: true, priority: 0, delay: 3600 })

Answer

rs.add('newhost:27017'); rs.reconfig({ _id: 'rs0', members: [ { _id: 0, host: 'existing1:27017' }, { _id: 1, host: 'existing2:27017' }, { _id: 2, host: 'existing3:27017' }, { _id: 3, host: 'newhost:27017', hidden: true, priority: 0, slaveDelay: 3600 } ] })

Question 2

A DBA is planning to upgrade a sharded cluster from MongoDB 4.4 to 5.0. The cluster has three shards, each a three-member replica set, and two config servers (also a replica set). The DBA must ensure a smooth upgrade with minimal downtime. Which two prerequisites must be met before starting the upgrade? (Choose two.)

Accepted Answer

All shards and config servers must be running MongoDB 4.4.. The two prerequisites for upgrading a sharded cluster from 4.4 to 5.0 are that all shards and config servers must be running MongoDB 4.4, and the featureCompatibilityVersion must be set to "4.4" on all components. These ensure that the cluster is in a consistent state and that the upgrade path is supported. Other steps like stopping the balancer or upgrading clients are recommended but not required.

Answer

Each shard must have at least one secondary with zero replication lag.

Answer

All clients must be upgraded to the MongoDB 5.0 drivers.

Answer

The balancer must be stopped before upgrading any shard.

Question 3

A DBA is configuring a new MongoDB 6.0 replica set for a production environment. The security policy requires that all client connections use TLS/SSL and that the replica set members authenticate each other using x.509 certificates. The DBA has already obtained valid certificates for each server and the clients. Which TWO mongod configuration options are required to enable both TLS for client connections and internal x.509 authentication? (Choose two.)

Accepted Answer

security.clusterAuthMode set to x509. To require TLS for all connections, net.tls.mode must be set to requireTLS. To enable x.509 authentication between replica set members, security.clusterAuthMode must be set to x509. These two settings together satisfy the policy. Other options either support TLS but do not enable it, or relate to client authorization or LDAP, which are not required here.

Answer

security.authorization set to enabled

Answer

net.tls.CAFile set to the CA certificate path

Answer

security.ldap.authz.queryTemplate set to a valid template

Question 4

A MongoDB DBA is investigating a replica set where the primary is experiencing high write latency. The DBA suspects that the write concern is causing delays. Which TWO of the following write concerns would require acknowledgment from a majority of voting members before returning success? (Choose two.)

Accepted Answer

{ w: 2 }. The write concerns that require acknowledgment from a majority of voting members are { w: 'majority' } and, in a typical three-member replica set, { w: 2 } because two out of three is a majority. The w: 'majority' option dynamically adjusts to the number of voting members, while w: 2 is a fixed number that may not always be a majority in larger sets. The other options either do not wait for majority acknowledgment or are invalid. (Explanation length: 70 words)

Answer

{ w: 0 }

Answer

{ w: 1 }

Answer

{ w: 'all' }

Question 5

A DBA needs to automate log rotation on a Linux-based MongoDB server without restarting the mongod process. Which signal or command should be used to ensure the current log file is archived and a new one is started?

Accepted Answer

Send a SIGUSR1 signal to the mongod PID.. Log rotation is a critical administrative task that prevents disk space exhaustion and facilitates log analysis. Using the SIGUSR1 signal on Linux systems allows the administrator to rotate logs without any downtime or server restarts. This ensures continuous availability while maintaining manageable file sizes for diagnostic purposes, which is essential for long-term server health and compliance with retention policies.

Answer

Send a SIGHUP signal to the mongod PID.

Answer

Run the 'rotateLogs' command from the admin database.

Answer

Update the 'systemLog.path' in the YAML config and run 'mongod --reconfig'.

Question 6

When enabling access control on a production sharded cluster, what is the most secure method for ensuring internal authentication between cluster components such as mongos and mongod instances?

Accepted Answer

Deploying X.509 certificates for member authentication.. Internal authentication ensures that only trusted components can join the cluster and communicate with each other. While keyfiles are common, X.509 certificates provide a higher level of security by utilizing a Certificate Authority (CA) and providing stronger identity verification. This is standard practice in high-security environments where protecting the internal traffic between nodes is as vital as client-to-server security.

Answer

Using a shared keyfile with 600 permissions.

Answer

Enabling SCRAM-SHA-256 for all administrative users.

Answer

Configuring LDAP authorization for the __system user.

Question 7

A developer reports slow queries on a specific collection. You decide to enable the database profiler to capture only queries taking longer than 200ms. Which command configuration achieves this?

Accepted Answer

db.setProfilingLevel(1, { slowms: 200 }). The database profiler is an essential administrative tool for diagnosing performance issues. Profiling level 1 is used to capture 'slow' operations without the overhead of capturing every single request (level 2). Setting the 'slowms' threshold to 200 allows the DBA to filter out expected noise and focus on the problematic operations.

Answer

db.setProfilingLevel(2, { slowms: 200 })

Answer

mongod --profile 200 --slowms 1

Answer

db.adminCommand({ profile: 0, slowms: 200 })

Question 8

In a dedicated server environment, what is the primary reason an administrator would choose to manually decrease the 'storage.wiredTiger.engineConfig.cacheSizeGB' below the default value?

Accepted Answer

To accommodate other processes or containers running on the same host.. Effective memory management is the core of MongoDB server administration. While the default cache size is usually optimal, administrators must adjust it when the server hosts other memory-intensive processes. If the operating system or other tools are starved for RAM, it can lead to excessive swapping and system instability, which harms database performance.

Answer

To increase the speed of BSON document compression.

Answer

To allow more memory for the filesystem cache to store indexes.

Answer

To reduce the size of the oplog on the primary node.

Question 9

Which THREE metrics provided by the 'mongostat' utility are most helpful for identifying a performance bottleneck caused by a high volume of concurrent write operations?

Accepted Answer

insert. Monitoring server health via mongostat is a daily task for a DBA. High write volumes are best identified by looking at the actual operation counts (insert, update, delete) and the state of the write queue. If the 'qw' (queue write) count is high, it indicates that the storage engine cannot keep up with the incoming write requests.

Answer

getmore

Answer

vsize

Question 10

A security audit requires that sensitive document data contained in query parameters must not be written to the MongoDB system logs. Which server configuration setting should be enabled?

Accepted Answer

security.redactClientLogData: true. Security administration involves protecting data at rest, in transit, and in logs. Log redaction is a feature that prevents sensitive information, like the contents of a 'find' filter or an 'insert' document, from appearing in the server logs. This is essential for compliance with regulations like GDPR, HIPAA, or PCI-DSS.

Answer

security.authorization: enabled

Answer

operationProfiling.mode: off

Answer

storage.wiredTiger.collectionConfig.blockCompressor: zlib

Question 11

Refer to the exhibit. An administrator attempts to recover a corrupted standalone mongod instance using the --repair flag. Based on the error log output, what is the most appropriate next step for the administrator?

Accepted Answer

Restore the data files from the most recent known-good backup.. The --repair flag is a last-resort tool that attempts to salvage data from corrupted files, but it cannot fix severe filesystem or metadata corruption where blocks are missing or unreadable. The 'Short read' error indicates physical or logical corruption that WiredTiger cannot bypass. In this scenario, restoring from a known-good backup is the only reliable way to ensure data integrity.

Answer

Run the --repair command again with the --wiredTigerEngineConfig option.

Answer

Delete the mongod.lock file and restart the server normally.

Answer

Manually edit the WiredTiger.wt file to fix the offset error.

Question 12

A server has multiple network interfaces including a public IP and a private management IP. How should the 'net.bindIp' configuration be managed to follow security best practices?

Accepted Answer

List only the loopback address and the specific internal IP addresses.. Binding MongoDB to the correct network interfaces is a fundamental security task. By default, older versions might bind to all interfaces, exposing the database to the public internet. Best practices dictate binding only to the loopback address and specific internal management or application network IPs to minimize the attack surface.

Answer

Set 'net.bindIp' to '0.0.0.0' to allow connections from any interface.

Answer

Leave 'net.bindIp' blank to let MongoDB choose the fastest interface.

Answer

Use the 'net.bindIpAll' setting to simplify the configuration.

Question 13

During a peak load period, the 'page faults' metric in mongostat increases significantly. What is the most likely administrative cause related to server resources?

Accepted Answer

The working set exceeds the available physical RAM.. Page faults occur when the mongod process attempts to access data that is not currently in the physical RAM (resident memory). While some page faults are normal, a sudden spike usually indicates that the 'working set' (the data and indexes accessed most frequently) has grown larger than the available RAM, forcing frequent disk reads.

Answer

The number of concurrent connections has reached the 'maxConns' limit.

Answer

The CPU is throttled due to excessive BSON serialization.

Answer

The journaling frequency is set too high for the disk subsystem.

Question 14

An administrator needs to create a restricted user for a third-party monitoring tool. The user must be able to perform backups and monitor server status but cannot read actual document data. Which TWO built-in roles should be combined?

Accepted Answer

backup. MongoDB's Role-Based Access Control (RBAC) allows for granular permission management. The 'backup' role provides the necessary privileges to use tools like mongodump without granting general read access to all collections. The 'clusterMonitor' role allows the user to run commands like 'serverStatus' and 'top', which are essential for monitoring performance.

Answer

readAnyDatabase

Answer

dbAdmin

Answer

hostManager

Question 15

A DBA executes 'mongodump --oplog' against a primary node in a replica set. What is the specific purpose of the --oplog flag in this administrative context?

Accepted Answer

It captures changes during the dump for point-in-time consistency.. When backing up a live database, data changes while the backup is running. The '--oplog' flag tells mongodump to capture all operations that occur during the dump process. This allows the DBA to restore the database to a consistent state by replaying those operations during the 'mongorestore' process, ensuring data integrity.

Answer

It exports the entire oplog collection into a separate BSON file.

Answer

It speeds up the dump process by reading from the oplog instead of collections.

Answer

It automatically compresses the output using the oplog's compression ratio.