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How to Encrypt/Decrypt SSH Keys for Deployment

Adding an encrypted SSH key to your project so Travis-CI can deploy your App automatically.

Why?

Continuous Deployment completely automates the process of deploying the latest version of the project/application to a given environment. This saves a considerable amount of time for the team as there are no manual steps to perform each time a new feature or bug-fix needs to be deployed, and avoids confusion around which version is on the given instance.

Many people prefer to use SSH-based deployment tools (such as Edeliver) because they are simple, fast and secured by the encrypted SSH "tunnel".

What?

A secure way to setup your "deployment pipeline" using Travis-CI to ship your App to (one or more) server instance(s) via SSH.

Is it "Secure"?

The SSH key is created and encrypted and is never transmitted in plaintext. Only Travis-CI can decrypt the key.

Note: if you are using the paid version of Travis-CI, you can use the Web-UI to add an SSH Key.
see: https://docs.travis-ci.com/user/private-dependencies
via: https://stackoverflow.com/questions/27444891/how-to-add-ssh-key-in-travis-ci

Who?

This guide is intended for:

  • People who have "outgrown Heroku" (the easy way to deploy apps...) or whose project/client/manager does not allow them to use Heroku.
  • Anyone who wants/needs "full control" over their deployment/platform.
  • Eager-beavers who are curious about "DevOps".

How?

Step "0": Before You Start (Prerequisites)

This guide assumes you already have a Linux "Virtual Private Server" (VPS) instance on a "Cloud" service provider e.g: AWS, Google Cloud, Digital Ocean, Linode, etc.

You will need SSH access to the instance and a note of the IP address so that you can login and perform the actions described below.

For the purposes of this walkthrough, we are using an CentOS instance running on DigitalOcean, however we have tested it on an Ubuntu instance running on both AWS, Azure and Linode and it works great!

If you do not already have a Digital Ocean account, please use the following ("referral") link to register: https://m.do.co/c/29379863a4f8 and get $10 in Credit.

No other knowledge is assumed. All commands are explained, however if anything is unclear, as always, we are "here + happy to help"; just open an issue on: https://github.com/dwyl/learn-travis/issues

1. Log-in to Your Server Instance

Log-in to your server instance via SSH using the IP address:

ssh user@ip.add.ress.here

e.g:

ssh root@138.68.163.126

You should see the terminal prompt change to reflect the fact that you are logged into the server. e.g:

ssh-login

2. Create a new SSH Key

Change directory into the .ssh directory on the instance:

cd ~/.ssh
ssh-keygen -t rsa -b 4096 -C "TravisCIDeployKey"

Press [Enter] key to use the defaults for the filename and leave the password blank.1
You should see output in your terminal similar to this:

generate-ssh-key

1Having an RSA key without a password is "OK" for use as a key exclusively used for deployment on Travis-CI because the key will be encrypted using Travis' public key meaning that only Travis can decrypt it. given that we are "trusting" Travis-CI with the private key there is not much point adding password to it, because the password can easily be "stripped" once the key is decrypted and given that Travis needs to "know" the password in order to use the key, if an "attacker" was to gain access to Travis' system and had their private key, the Internet would "break"! Seriously, enough NPM packages are automatically published by Travis-CI that it would be "left-pad gate" times a million if Travis were compromised! However, if you have time to help us with "upgrading" this tutorial to use an RSA key with a password we would love to know how it's done see: dwyl#42 (comment)

2.1 Add the new SSH Key to the authorized_keys File

In order for this key to be used for SSH access, it needs to be included in the authorized_keys file on the server.

Run the following command to append the public key to the list of "authorized keys":

cat id_rsa.pub >> authorized_keys

We will test that this worked below in step 3.1

3. Securely Download the SSH Key

Ensure that your current working directory is the project/app that you are adding the SSH key for. (so you don't have to move the key later)

before you download the SSH key, first add a line to your .gitignore file to ensure that you don't accidentally commit the private key in plaintext!

echo "deploy_key" >> .gitignore

With that done, download the key with the following command:

scp user@ip.add.ress.here:/root/.ssh/id_rsa  ./deploy_key

e.g:

scp root@138.68.163.126:/root/.ssh/id_rsa ./deploy_key

download-ssh-key

3.1 Test That you are Able to Login to the Server ...

Test that you are able to login to the server using the deploy_key:

ssh -i /path/to/deploy_key user@ip.add.ress.here

e.g: 

ssh -i ./deploy_key root@138.68.163.126

ssh-login-with-deploy_key

4. Install Travis-CI CLI

In order to encrypt both the SSH key and passphrase, we will need the Travis-CI CLI

Install the Travis CLI on your localhost (to avoid "polluting" the server and so that you can use it in future projects):

gem install travis

You should see: travis-installed-localhost

if you see the error:

-bash: gem: command not found

You need to install ruby first.

Mac

brew install ruby

Centos (or RedHat/Fedora)

sudo yum install ruby -y

You should see:
image

Now try installing the Travis-CI CLI again.

Ubuntu

sudo apt-get install ruby-full

For installation instructions for specific/different Linux distribution,
see: https://www.ruby-lang.org/en/documentation/installation

Windows...?


But seriously, install Linux on your Windows PC and set yourself free! https://www.computerworld.com/article/3252823/linux/why-linux-is-better-than-windows-or-macos-for-security.html

If you are "stuck" using windows see: https://rubyinstaller.org

5. Encrypt the Private Key

Use the travis CLI to encrypt the key on your localhost:

touch .travis.yml && travis encrypt-file ./deploy_key --add

You should see something like this:

ssh-key-encrypted

if you look at the .travis.yml file in your project folder, you will notice that a couple of lines were added:

before_install:
- openssl aes-256-cbc -K $encrypted_77965d5bdd4d_key -iv $encrypted_77965d5bdd4d_iv
  -in deploy_key.enc -out ./deploy_key -d

Ensure that you commit the deploy_key.enc file and .travis.yml file in your project before pushing to GitHub.

Note: there is an alternative way of doing this where the SSH key is to base64 encode the encrypted key and included it in .travis.yml, see: https://gist.github.com/lukewpatterson/4242707 but we feel that it adds a lot of "noise" to the .travis.yml file. Decide for yourself which you prefer; be consistent across your projects.

5.1 Set the RSA Key as the "preferred key" in .travis.yml

We already added the encrypted RSA key to our repository in step 5 (above) but we also need to add the RSA key as the "preferred key" on Travis-CI. To do that, add the following line to your .travis.yml file:

- ssh-add ./deploy_key

ensure that this line is after the key decryption line. Example: https://github.com/nelsonic/hello-world-node-http-server/blob/master/.travis.yml#L13

6. Test it on Travis-CI!

The "proof of the pudding" is confirming that Travis-CI can execute an SSH command on your server instance ...

Add the following lines to your .travis.yml file:

- eval "$(ssh-agent -s)"
- chmod 600 ./deploy_key
- echo -e "Host $SERVER_IP_ADDRESS\n\tStrictHostKeyChecking no\n" >> ~/.ssh/config
- ssh-add ./deploy_key
- ssh -i ./deploy_key root@138.68.163.126 pwd

Let's walkthrough those lines ...

  • eval "$(ssh-agent -s)" = start the ssh-agent (so that we can run ssh commands)
  • chmod 600 ./deploy_key = change permissions on deploy_key to avoid warnings.
  • echo -e "Host $SERVER_IP_ADDRESS\n\tStrictHostKeyChecking no\n" >> ~/.ssh/config = avoid Travis asking if we want to "check" the identity of our host (VPS) Via: https://stackoverflow.com/questions/16638573/auto-authorize-ssh-auth-requests-on-travis-ci
  • ssh-add ./deploy_key = add the deploy_key as our preferred ssh RSA key.
  • ssh -i ./deploy_key root@138.68.163.126 pwd = run the pwd command on the deployment server using the deploy_key as our "identity" file (RSA Key)

If the ssh command works on Travis-CI (which it should if you followed each step of this guide...) You should see something similar to the folloiwng output: https://travis-ci.org/nelsonic/hello-world-node-http-server/builds/385702903#L457 ssh-pwd-success-travis-ci

Full example (working) .travis.yml file.

Background / Related Reading