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Exam ANS-C00 topic 1 question 30 discussion

Exam question from Amazon's ANS-C00

Question #: 30
Topic #: 1

Your company uses an NTP server to synchronize time across systems. The company runs multiple versions of Linux and Windows systems. You discover that the NTP server has failed, and you need to add an alternate NTP server to your instances.
Where should you apply the NTP server update to propagate information without rebooting your running instances?

A. DHCP Options Set
B. instance user-data
C. cfn-init scripts
D. instance meta-data

Show Suggested Answer

Suggested Answer: A 🗳️

by HazemYousry at Sept. 27, 2019, 6:21 a.m.

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zues

Highly Voted 3 years, 7 months ago

ANS:A After you associate a new set of DHCP options with a VPC, any existing instances and all new instances that you launch in the VPC use these options. You don't need to restart or relaunch the instances. They automatically pick up the changes within a few hours, depending on how frequently the instance renews its DHCP lease. If you want, you can explicitly renew the lease using the operating system on the instance.

upvoted 19 times

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HazemYousry

Highly Voted 3 years, 8 months ago

Answer is A

upvoted 5 times

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PavanKushwah123

Most Recent 2 years, 5 months ago

Correct Answer C

upvoted 1 times

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Luck_Huang

2 years, 6 months ago

should be A. for C, the "cfn-init" helper scripts pre-installed on amaz Linux but may not on other platform/OS

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Marty2021

2 years, 11 months ago

Selected Answer: A

A is correct

upvoted 2 times

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neershah

3 years, 4 months ago

Selected Answer: A

A is the correct one, agree with Zues

upvoted 3 times

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Cyril_the_Squirl

3 years, 7 months ago

A is Correct.

upvoted 2 times

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ChauPhan

3 years, 7 months ago

Overview of DHCP options sets By default, all instances in a nondefault VPC receive an unresolvable host name that AWS assigns (for example, ip-10-0-0-202). You can assign your own domain name to your instances, and use up to four of your own DNS servers. To do that, you must create a custom set of DHCP options to use with the VPC. The following are the supported options for a DHCP options set, and the value that is provided in the default DHCP options set for your VPC. You can specify only the options that you need in your DHCP options set. For more information about the options ntp-servers The IP addresses of up to four Network Time Protocol (NTP) servers. For more information, see section 8.3 of RFC 2132. You can specify the Amazon Time Sync Service at 169.254.169.123. For more information, see Setting the time in the Amazon EC2 User Guide for Linux Instances.

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ChauPhan

3 years, 7 months ago

You can set ntp-servers in DHCP option sets, and don't need to reboot.

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ChauPhan

3 years, 7 months ago

A C needs reboot. A dont need

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2aldous

3 years, 7 months ago

The answer is A https://docs.aws.amazon.com/vpc/latest/userguide/VPC_DHCP_Options.html

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Cshekmen

3 years, 7 months ago

I would rather go with C: The "update behavior" for updating NTP using cfn-init script seems to be "Replacement", meaning the resource will be replaced and then new settings will be applied on new one. - it satisfies following requirement: propagate information without rebooting your running instances

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backfringe

3 years, 7 months ago

its A!

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ITstudy

3 years, 7 months ago

A is sure. We have such a setup.

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kvirk

3 years, 7 months ago

A is correct

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Ibranthovic

3 years, 7 months ago

A can't be true as it gives the information only on initiating the instance or after rebooting

upvoted 1 times

eeghai7thioyaiR4

3 years, 7 months ago

That is not true Informations given through DHCP have a specific duration, typicaly a couple of hours Once that time is nearly expired, the dhcp client (that lives on the EC2 instance) will try to renew the DHCP lease, sending a DHCP REQUEST which includes the previous informations (its IP etc) The DHCP server, managed by AWS, will sent it back a DHCP ACK (saying "you are ok for another couple of hours) If some options changed, the new values will be provided this way I do not know which time duration is used in EC2, but TLDR: changed a DHCP option set will change the data on the associated EC2 instance within a few hours, without rebooting anything Answer: A

upvoted 2 times

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Meetra

3 years, 8 months ago

ifcourse in the real world it would be both A and C . but C seems an immediate intervention.

upvoted 1 times

Tron09

3 years, 8 months ago

The "update behavior" for updating NTP using cfn-init script seems to be "Replacement", meaning the resource will be replaced and then new settings will be applied on new one. Refer: https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-resource-ec2-dhcp-options.html. In this case, I guess A is more preferable.

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Meetra

3 years, 8 months ago

C. cfn-init scripts it shouldn't be A. A means the NTP would be updated after few hours or whenever the lease time has expires. cfn int is a script you can run commands with whenever yo ulike.

upvoted 3 times

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