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Our Rails app is scaled at multiple machines, from time to time, we need to change settings at production.yml , right now we have to ssh into each server and do the editing at each machine individually.

What's the right way to handle this case?

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Configuration management systems like Puppet and Chef are made for this exact purpose.

If you don't want to use them, you can use a script to SCP the file to the server:

while read host; do
    scp -i yourKey production.yml user@$host:/destination/production.yml
    # Add an ssh command here if you need to restart any services
done <  hosts.txt; 
  • currently we are not using those tools, wouldn't this approach involve full deployment cycle ? we only need this particular sync – simo Jan 29 at 14:12
  • Not necessarily, there's nothing wrong with using them to deploy files outside of the development cycle. Although they might be overkill for something small like this. I've edited my answer – Farhan.K Jan 29 at 14:21
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    I would consider using one of these tools if I were you. It makes it much easier to manage multiple machines. – Farhan.K Jan 29 at 14:27
  • If there are any chances that those files will be changed by someone else after you modify them , thus causing a configuration drift , I would suggest going with @Farhan.K's suggestion as Puppet and Chef will check periodically if there has been any change to the file and if so , change it to what you define . If not , Puppet and Chef could have an overhead since they are agent based , and in this case I would strongly recommend using Ansible which is agentless and uses SSH to connect to managed hosts. You could manage one file and push it to managed hosts. good luck – John Doe Jan 29 at 16:20
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    @pizdelect it is not horrible, in fact it is recommended practice and The Correct Way® to read multiple lines from a file. What is horrible is the for line in $(cat file) construct which can fail very easily. See bash pitfall #1. Note that all files should be terminated by a newline, if you have files that don't, then that's a whole different problem, but that's not an issue with read. – terdon Feb 1 at 9:36
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Better to use rsync instead of scp. Advantages of rsync :

First, it will check whether any changes are there or not in source file when compared with file in destination. Only if there is a change then it will transfer so it will take less time and be faster when compared with scp.

while read host
do
    rsync -avzh production.yml userid@$host:/destination_location/production.yml
done < hosts.txt
  • using while read; do ... done < hosts.txt is horrible -- same comment as here. Also @terdon. – pizdelect Feb 1 at 9:21
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    @pizdelect no, it isn't. It is the best and safest way to read lines from a file. The absolute safest is while IFS= read -r var; do..., but this is not needed here. IN any case, using a while read loop instead of something truly awful such as for line in $(cat file) is both standard and the best practice recommended pretty much everywhere. Also see 1, 2, 3, 4, 5. – terdon Feb 1 at 9:42

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