How to generate random string at end of hostname?

Justin_Franks · July 19, 2014, 6:17pm

For every node we provision with knife ec2/openstack/etc… we want the hostnames to have a format of:

staticstring-staticstring-randomstring

Example: web-server-hk3dp99x

If the host reboots the name will not change.

For each newly provisioned node the random string will change.

Suggestions on the best approach?

Justin Franks
Lead Operations Engineer
SaaS, Cloud, Data Centers & Infrastructure
Lithium Technologies, Inc
225 Bush St., 15th Floor
San Francisco, CA 94104
tel: +1 415 757 3100 x3219

coderanger · July 19, 2014, 6:29pm

It is highly recommended you use the raw hostnames as generated by EC2/Nova. Trying to change the hostname from Chef is tricky even at the best of times. If you really do want to change it, I would recommend doing it before Chef is bootstrapped in your own provisioning system (cloud-init on EC2, for example).

--Noah

On Jul 19, 2014, at 11:17 AM, Justin Franks justin.franks@lithium.com wrote:

How to generate random string at end of hostname?
For every node we provision with knife ec2/openstack/etc... we want the hostnames to have a format of:
staticstring-staticstring-randomstring
Example: web-server-hk3dp99x
If the host reboots the name will not change.
For each newly provisioned node the random string will change.
Suggestions on the best approach?

Justin Franks
Lead Operations Engineer
SaaS, Cloud, Data Centers & Infrastructure
Lithium Technologies, Inc
225 Bush St., 15th Floor
San Francisco, CA 94104
tel: +1 415 757 3100 x3219

Guilhem_Lettron · July 21, 2014, 3:13pm

Hi Justin,

I created a simple golang project for this usecase:
GitHub - guilhem/bapteme: Naming network service (with gobuild link on it)
And a cookbook to install it: https://github.com/optiflows-cookbooks/bapteme

Any comment is welcome as I don't use it in production for the moment.

Guilhem Lettron

On Sat, Jul 19, 2014 at 8:29 PM, Noah Kantrowitz noah@coderanger.net
wrote:

It is highly recommended you use the raw hostnames as generated by
EC2/Nova. Trying to change the hostname from Chef is tricky even at the
best of times. If you really do want to change it, I would recommend doing
it before Chef is bootstrapped in your own provisioning system (cloud-init
on EC2, for example).

--Noah

On Jul 19, 2014, at 11:17 AM, Justin Franks justin.franks@lithium.com
wrote:

How to generate random string at end of hostname?
For every node we provision with knife ec2/openstack/etc... we want the
hostnames to have a format of:
staticstring-staticstring-randomstring
Example: web-server-hk3dp99x
If the host reboots the name will not change.
For each newly provisioned node the random string will change.
Suggestions on the best approach?

Justin Franks
Lead Operations Engineer
SaaS, Cloud, Data Centers & Infrastructure
Lithium Technologies, Inc
225 Bush St., 15th Floor
San Francisco, CA 94104
tel: +1 415 757 3100 x3219

Matt_Ray_GETCHEF · July 21, 2014, 3:15pm

I'd agree with Noah, some platforms don't provide names though. Here's
the hacky generator used by knife-openstack and others through
knife-cloud:

github.com

chef/knife-cloud/blob/main/lib/chef/knife/cloud/server/create_command.rb#L126


      
                  def set_default_config
                    config[:image_os_type] = "windows" if config[:connection_protocol] == "winrm"
                  end
          
                  # generate a random name if chef_node_name is empty
                  def get_node_name(chef_node_name, prefix)
                    return chef_node_name unless chef_node_name.nil?
          
                    # lazy uuids, 15 chars cause windows has limits
                    ("#{prefix}-" + rand.to_s.split(".")[1]).slice(0, 14)
                  end
          
                  def post_connection_validations; end
                end # class ServerCreateCommand
              end
            end
          end

Thanks,
Matt Ray
Director of Partner Integration :: Chef
512.731.2218 :: matt@getchef.com
mattray :: GitHub :: IRC :: Twitter

On Sat, Jul 19, 2014 at 1:29 PM, Noah Kantrowitz noah@coderanger.net wrote:

It is highly recommended you use the raw hostnames as generated by EC2/Nova. Trying to change the hostname from Chef is tricky even at the best of times. If you really do want to change it, I would recommend doing it before Chef is bootstrapped in your own provisioning system (cloud-init on EC2, for example).

--Noah

On Jul 19, 2014, at 11:17 AM, Justin Franks justin.franks@lithium.com wrote:

How to generate random string at end of hostname?
For every node we provision with knife ec2/openstack/etc... we want the hostnames to have a format of:
staticstring-staticstring-randomstring
Example: web-server-hk3dp99x
If the host reboots the name will not change.
For each newly provisioned node the random string will change.
Suggestions on the best approach?

Justin Franks
Lead Operations Engineer
SaaS, Cloud, Data Centers & Infrastructure
Lithium Technologies, Inc
225 Bush St., 15th Floor
San Francisco, CA 94104
tel: +1 415 757 3100 x3219

Seth_Vargo2 · July 21, 2014, 8:35pm

ruby -e "require 'securerandom'; puts SecureRandom.hex(3)"

Seth

On Jul 21, 2014, at 11:15 AM, Matt Ray matt@getchef.com wrote:

I'd agree with Noah, some platforms don't provide names though. Here's
the hacky generator used by knife-openstack and others through
knife-cloud:
https://github.com/opscode/knife-cloud/blob/master/lib/chef/knife/cloud/server/create_command.rb#L126

Thanks,
Matt Ray
Director of Partner Integration :: Chef
512.731.2218 :: matt@getchef.com
mattray :: GitHub :: IRC :: Twitter

On Sat, Jul 19, 2014 at 1:29 PM, Noah Kantrowitz noah@coderanger.net wrote:

It is highly recommended you use the raw hostnames as generated by EC2/Nova. Trying to change the hostname from Chef is tricky even at the best of times. If you really do want to change it, I would recommend doing it before Chef is bootstrapped in your own provisioning system (cloud-init on EC2, for example).

--Noah

On Jul 19, 2014, at 11:17 AM, Justin Franks justin.franks@lithium.com wrote:

How to generate random string at end of hostname?
For every node we provision with knife ec2/openstack/etc... we want the hostnames to have a format of:
staticstring-staticstring-randomstring
Example: web-server-hk3dp99x
If the host reboots the name will not change.
For each newly provisioned node the random string will change.
Suggestions on the best approach?

Justin Franks
Lead Operations Engineer
SaaS, Cloud, Data Centers & Infrastructure
Lithium Technologies, Inc
225 Bush St., 15th Floor
San Francisco, CA 94104
tel: +1 415 757 3100 x3219

Justin_Franks · July 21, 2014, 9:17pm

Seth,
Where does this Ruby go? Where do I "puts" it?

Justin Franks
Lead Operations Engineer
SaaS, Cloud, Data Centers & Infrastructure
Lithium Technologies, Inc
225 Bush St., 15th Floor
San Francisco, CA 94104
tel: +1 415 757 3100 x3219

From: Seth Vargo sethvargo@getchef.com
Sent: Monday, July 21, 2014 1:35 PM
To: chef@lists.opscode.com
Subject: [chef] Re: How to generate random string at end of hostname?

ruby -e "require 'securerandom'; puts SecureRandom.hex(3)"

Seth

On Jul 21, 2014, at 11:15 AM, Matt Ray matt@getchef.com wrote:

I'd agree with Noah, some platforms don't provide names though. Here's
the hacky generator used by knife-openstack and others through
knife-cloud:
https://github.com/opscode/knife-cloud/blob/master/lib/chef/knife/cloud/server/create_command.rb#L126

Thanks,
Matt Ray
Director of Partner Integration :: Chef
512.731.2218 :: matt@getchef.com
mattray :: GitHub :: IRC :: Twitter

On Sat, Jul 19, 2014 at 1:29 PM, Noah Kantrowitz noah@coderanger.net wrote:

It is highly recommended you use the raw hostnames as generated by EC2/Nova. Trying to change the hostname from Chef is tricky even at the best of times. If you really do want to change it, I would recommend doing it before Chef is bootstrapped in your own provisioning system (cloud-init on EC2, for example).

--Noah

On Jul 19, 2014, at 11:17 AM, Justin Franks justin.franks@lithium.com wrote:

How to generate random string at end of hostname?
For every node we provision with knife ec2/openstack/etc... we want the hostnames to have a format of:
staticstring-staticstring-randomstring
Example: web-server-hk3dp99x
If the host reboots the name will not change.
For each newly provisioned node the random string will change.
Suggestions on the best approach?

Justin Franks
Lead Operations Engineer
SaaS, Cloud, Data Centers & Infrastructure
Lithium Technologies, Inc
225 Bush St., 15th Floor
San Francisco, CA 94104
tel: +1 415 757 3100 x3219

Tony_Burns · July 21, 2014, 9:29pm

Justin,

If you have a Ruby script that’s setting the hostname for you before Chef runs, you could just interpolate what Seth said into your hostname like:

#!/opt/chef/embedded/bin/ruby

set_hostname.rb

require ‘secure random’

hostname_template = ARGV[0]
hostname_id = SecureRandom.hex(3)
hostname = “#{hostname_template}-#{hostname_id}”

File.open(‘/etc/hosts’, ‘a’) do |file|
file.write "127.0.0.1 localhost #{hostname}"
end

File.open(‘/etc/hostname’, ‘w’) do |file|
file.write hostname
end

system(‘service hostname start’)

Cheers,

Tony

On Jul 21, 2014, at 5:17 PM, Justin Franks justin.franks@lithium.com wrote:

Seth,
Where does this Ruby go? Where do I "puts" it?

Justin Franks
Lead Operations Engineer
SaaS, Cloud, Data Centers & Infrastructure
Lithium Technologies, Inc
225 Bush St., 15th Floor
San Francisco, CA 94104
tel: +1 415 757 3100 x3219

From: Seth Vargo sethvargo@getchef.com
Sent: Monday, July 21, 2014 1:35 PM
To: chef@lists.opscode.com
Subject: [chef] Re: How to generate random string at end of hostname?

ruby -e "require 'securerandom'; puts SecureRandom.hex(3)"

Seth

On Jul 21, 2014, at 11:15 AM, Matt Ray matt@getchef.com wrote:

I'd agree with Noah, some platforms don't provide names though. Here's
the hacky generator used by knife-openstack and others through
knife-cloud:
https://github.com/opscode/knife-cloud/blob/master/lib/chef/knife/cloud/server/create_command.rb#L126

Thanks,
Matt Ray
Director of Partner Integration :: Chef
512.731.2218 :: matt@getchef.com
mattray :: GitHub :: IRC :: Twitter

On Sat, Jul 19, 2014 at 1:29 PM, Noah Kantrowitz noah@coderanger.net wrote:

It is highly recommended you use the raw hostnames as generated by EC2/Nova. Trying to change the hostname from Chef is tricky even at the best of times. If you really do want to change it, I would recommend doing it before Chef is bootstrapped in your own provisioning system (cloud-init on EC2, for example).

--Noah

On Jul 19, 2014, at 11:17 AM, Justin Franks justin.franks@lithium.com wrote:

How to generate random string at end of hostname?
For every node we provision with knife ec2/openstack/etc... we want the hostnames to have a format of:
staticstring-staticstring-randomstring
Example: web-server-hk3dp99x
If the host reboots the name will not change.
For each newly provisioned node the random string will change.
Suggestions on the best approach?

Justin Franks
Lead Operations Engineer
SaaS, Cloud, Data Centers & Infrastructure
Lithium Technologies, Inc
225 Bush St., 15th Floor
San Francisco, CA 94104
tel: +1 415 757 3100 x3219

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How to generate random string at end of hostname?

set_hostname.rb

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