# Best Practice -- Connecting Hawk to the world

Hawk is surrounded by a strict outgoing firewall. Users can not open arbitrary connections to hosts on the internet. Connections can only be established through a proxy host. This document describes how to set up a proxy, and how to use this proxy in a number of common use cases.

Common use cases include:
  - working on remote repositories with git
  - installing Python packages from PyPi, etc 
  - access to package registries for languages such as Golang, Rust, etc.


When following this guide, you will have to execute actions or command on Hawk, but also on your local workstation or laptop. For clarity, examples below will use prompts `local>` and `hawk>`, respectively.


## Setting up a proxy with ssh

Please note, that there is numerous ways to set up proxies. However, HLRS only supports the method describe in the following.

Ssh allows to create reverse tunnels from Hawk back to your local machine. In addition, it can run a proxy, more specifically a SOCKS5 proxy, on the local end of this tunnel. SOCKS5 is a widely supported standard which allows many applications to use such proxies to connect to remote hosts.

Note however, that the tunnel is open on the remote side. Every user on Hawk will be able to use the tunnel and thus have a network connection to your local network. We strongly suggest to keep the tunnel open only when necessary.

Tunnels are associated to _ports_. In the following, you will have to specify a port which is referred by the environment variable `$MY_PROXY_PORT`. You may choose the port numbers freely in the suggested range 10000 to 60000. It may happen, that a port is currently used by another user ... just choose a different one.

Ok, let's do it.

The following will open a regular ssh connection to Hawk. In addition, the argument `-D $MY_PROXY_PORT` will establish a reverse dynamic port forwarding tunnel which opens at port `$MY_PROXY_PORT` on the Hawk side and connects to a SOCKS5 proxy on your local side.  
```bash
local> MY_PROXY_PORT=XXXX   # choose a port number between 10000 and 60000
local> ssh -D $MY_PROXY_PORT hawk.hww.hlrs.de
```

The tunnel will remain open as long as the connection to Hawk is open. The tunnel will close as soon as your connection closes. Please note, that we do recommend to _not use_ command line arguments to keep the connection open in the background as you may loose track of open reverse tunnels.

Once you proxy is established, you may proceed to use it for various tasks.


## HTTPS/HTTP proxy variables

Requirements:
  - set up a proxy with ssh as describe in [this section](#setting-up-a-proxy-with-ssh)

Most applications which support https or http protocols can use proxies. Most of them will take the proxy from the environment variables `$https_proxy` and `$http_proxy`. Sometimes, you will have to specify the proxy through command line arguments.

Example usage:
```bash
# set up proxy with ssh and continue in the terminal which just opened 
hawk> MY_PROXY_PORT=XXXX      # choose same port as above

hawk> curl ifconfig.me        # timeout, no connection to internet

hawk> curl --proxy socks5://localhost:$MY_PROXY_PORT        # specify proxy through command line argument

hawk> export https_proxy=socks5://localhost:$MY_PROXY_PORT  # set proxy environment variables
hawk> export http_proxy=$https_proxy
hawk> curl ifconfig.me

hawk> # close terminal to close reverse tunnel when done
```

Most of the other use cases will build on the usage of these environment variables. Therefore we recommend to set them in you `.bashrc`. ==**TODO: do we recommend this?**==


## Installing Python packages with pip

Requirements:
  - set up a proxy with ssh as describe in [this section](#setting-up-a-proxy-with-ssh)
  - set https proxy variables as describe in [this section](#httpshttp-proxy-variables)

Python's package manager `pip` will honour proxy settings through environment variables or command line arguments. However, it will need the package `pysocks` to do so. Unfortunately, `pysocks` is not a part of the core of Python and you may end up without it (for instance if you create a Python environment without including the system site-packages). Note, that you might have to add the command line argument `--user` to pip commands below.

```bash
# set up proxy with ssh and continue in the terminal which just opened 
hawk> MY_PROXY_PORT=XXXX            # choose same port as above

hawk> python3 -m pip install six    # timeout, no connection to internet

hawk> python3 -m pip --proxy socks5://localhost:$MY_PROXY_PORT

# set https/http proxy environment variables as describe above, then
hawk> python3 -m pip install six
```

If you get error messages related to missing SOCKS5 support in pip, do
```bash
# set up proxy with ssh and continue in the terminal which just opened
# set https/http proxy environment variables as describe above, then

hawk> python3 -m pip install /sw/general/x86_64/development/python/share/PySocks-1.7.1-py3-none-any.whl
```


## Using proxy with git

Git essentially supports two [protocols](https://git-scm.com/book/en/v2/Git-on-the-Server-The-Protocols) for communication with remote repositories:
  - HTTP protocol
  - SSH protocol

Both protocols can routed through a SOCKS5 proxy.

==**TODO: do we recommend one over the other?**==


### Git HTTP protocol

Requirements:
  - set up a proxy with ssh as describe in [this section](#setting-up-a-proxy-with-ssh)
  - set https proxy variables as describe in [this section](#httpshttp-proxy-variables)

The HTTP protocol is mostly used to clone public git repositories for read-only access (without the intension to push changes upstream). In these cases, git does not use any kind of authentication. However, git can also use authentication through the HTTP protocol.

In the simplest case, cloning public repositories without authentication just requires setting up the SOCKS5 proxy and defining the https/http proxy environment variables as explained above. Then just clone with
```bash
# set up proxy with ssh and continue in the terminal which just opened 
# set https/http proxy environment variables as describe above, then
hawk> git clone https://github.com:user/project.git

hawk> git pull
```

To access remote repositories with authentication, we recommend using _access tokens_. These access tokens are supported my most repositories. Follow the links to the respective documentation: [github](https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/managing-your-personal-access-tokens), gitlab, [gitea](https://docs.codeberg.org/advanced/access-token/), etc. 

We recommend to set up dedicated access tokens for access from Hawk. Then work on the repository with 
```bash
# set up proxy with ssh and continue in the terminal which just opened 
# set https/http proxy environment variables as describe above, then
# set up access tokens for repository
hawk> git clone https://github.com:user/project.git
# enter user name
# enter access token as password

hawk> git fetch
hawk> git pull
hawk> git push
```
Any of these commands may ask you for credentials such as username and password. Enter your access code when prompted for the password. You may consider [managing credentials in git](https://git-scm.com/docs/gitcredentials).


### Git with SSH protocol

Requirements:
  - set up a proxy with ssh as describe in [this section](#setting-up-a-proxy-with-ssh)

The other protocol for accessing remote git repositories is the SSH protocol. Repository URLs for this protocol in general look like
```bash
[user@]server:[somepath/]project.git
```
On github.com, for instance, it is
```bash
git@github.com:user/project.git
```

Repositories like these require to authenticate with an ssh public key. We recommend to create a dedicated key for access to the repository from Hawk, and to register (upload) it with the repository. The following will assume the public key file is name `repo_from_hawk.pub`.

When using the SSH protocol, git will start ssh to establish a connection from Hawk to the repository server (e.g. github) but fail. Instead, you need to tell ssh to routed the connection through your reverse tunnel, the one you have set up [above](#setting-up-a-proxy-with-ssh). The easiest is to add the following to your ssh configuration file (`.ssh/config`):

```bash
Host github.com
  # replace XXXX below with port number of your reverse tunnel
  ProxyCommand  ncat %h %p --proxy localhost:XXXX --proxy-type=socks5
  IdentityFile ~/.ssh/repo_from_hawk
  PasswordAuthentication no
```
Replace the `XXXX` above with the port number of your reverse tunnel, i.e. `$MY_PROXY_PORT` in the instructions above. Please note, that the proxy command above works on Hawk, but may fail on other systems. In particular, there is various versions of the _netcat_ utility, all of which use different command line arguments.

Now all operations on remote git repositories should work as long as your reverse tunnel is up
```bash
git clone git@github.com:user/project.git
git fetch 
git pull
git push
```
Any of these commands my ask you for credentials to unlock the ssh public key.

Again, we recommend to keep the reverse tunnel open as briefly as possible.