DEV/Chaining Git Over SSH

Accessing public repo from within DMZ machine

Problem:

Your development machine is a lab machine in DMZ. However, you need to access some git repo (gerrit.fd.io) that you cannot directly clone onto a lab-development machine. How to achieve it ?

Rudimentary Solution:

Clone the repo onto a machine (say laptop) that can access gerrit.fd.io and scp it to the lab-development machine.

Issues:

1. For any change you wish to send out for review, you need to create a patch and patch the repo on your laptop.
2. In the mean time, if remote-repo is modified, you need to do a git pull. Unfortunately, you cannot as your lab-development machine is in DMZ.
3. Many other git commands cannot be used and I do not go over them here.

Solution: SSH Chaining.

The following solution description takes gerrit.fd.io as an example. One can extend this solution to any other code repo or even for multi-hop ssh.

• First you need a system from where you have access to gerrit.fd.io . For our documentation here, lets call hostname as mystery and username as arcane.
• Create a ssh-key pair using ssh-keygen to enable password-less ssh login. For details 'man ssh-keygen'. The below command generates two files multihop.rsa and multihop.rsa.pub in ~/.ssh directory. multihop.rsa.pub is a public key and multihop.rsa is a private key. Details: Public Key Cryptography. NOTE: This step is optional if you already have a pair of keys, which you would like to use.

 ssh-keygen -C "SSH key for multi-hop for arcane" -f ~/.ssh/multihop.rsa -N ""
 
 -C: Comment
 -f: ouput filename
 -N: passphrase; using "" is fine.

• Login to mystery as arcane and append contents of multihop.rsa.pub to ~/.ssh/authorized_keys. By doing so, mystery will allow password-less ssh login when corresponding private key is used, which you will specify in the next step on the lab-development machine from where you login.

• Edit ~/.ssh/config on the lab-development machine and add the following:

 Host mystery
   User arcane
   IdentityFile ~/.ssh/multihop.rsa
 
 # Should have port on the first line
 Host gerrit.fd.io
   ProxyCommand ssh -q mystery nc gerrit.fd.io 29418
   User <gerrit username>
   IdentityFile <path to gerrit identity private key on lab-development machine>

How to get access to gerrit ? Obtain VPP Source Code

Now you should be able to perform your favorite git operations.

 git clone ssh://gerrit.fd.io/vpp.git
 Cloning into 'vpp'...
 remote: Counting objects: 986, done
 remote: Finding sources: 100% (41/41)
 remote: Total 1655 (delta 0), reused 1626 (delta 0)
 Receiving objects: 100% (1655/1655), 2.66 MiB | 1.42 MiB/s, done.
 Resolving deltas: 100% (651/651), done.
 Checking connectivity... done.

There was no need to specify username and port on the command line as you have added them in ~/.ssh/config.