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Software SysAdmin

Setting NIC IP addresses as environment variables

An easy and reliable method for applying your NIC IP addresses to your environment and scripts.

For me, most any work day consists of Ubuntu Server, Docker, Ansible, Python, and Golang; but not all server instances have Static IP addresses, some only have an Ephemeral IP address. When I need to pass an interface’s address to systemd, shell script, Docker, Kubernetes, etc. without having to perform edits on code or configuration, this can become problematic.

An easy way to do so is with setup-network-environment via system initialization and optionally, VPN connection parameters (e.g. OpenVPN’s up and down options). Running this program will produce (and subsequently update) an environment file (by default, located at /etc/network-environment) that can be parsed by Bash, systemd, and others, in order to populate variables.

An example of the generated environment file:

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LO_IPV4=127.0.0.1
ENO16777736_IPV4=192.168.12.10
DEFAULT_IPV4=192.168.12.10
TUN0_IPV4=172.16.12.10

Prerequisites

In this article, I’ll assume that these prerequisites haven’t been fulfilled (Snappy, Git, and Go aren’t part of the standard install for Ubuntu Server 16 LTS), and will cover those installation processes as well.

Setup

Update the package cache:

sudo apt update

Set ~/.bashrc to be loaded by ~/.bash_profile:?

echo 'source $HOME/.bashrc' >> $HOME/.bash_profile

Snappy

Since Ubuntu 18.04 and later include Snappy, you can skip this step if this is what you’re using.

Install Snappy:

sudo apt install --yes snapd

Toolkit

Install build tools and Git:

sudo apt install --yes \
    build-essential \
    git \
    ;

Golang

After you perform this step, please logout, and log back in. If you don’t, Golang will not properly function for the next step.

Install the latest version of Golang:

snap install --classic go

The reason that I set $GOBIN to /usr/local/bin is because I want Go-based binaries to be accessible by the entire system. In a multi-user environment, your needs may differ, and plenty of people use $GOPATH/bin, and update $PATH, to reflect these utilities existing in their home directories.

That said, there’s plenty of discussion on the Internet about what this should be set to 1 2, so, YMMV.

Furthermore, the reason that I don’t simply call source /etc/network-environment, is due to Bash not being able to parse variables with dashes in them (this seems to happen on particular Linux instances.)

Append environment variables to ~/.bashrc:

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cat << 'EOF' | tee --append $HOME/.bashrc > /dev/null
# Golang
export GOPATH=$HOME/go
export GOBIN=/usr/local/bin
export PATH=$GOBIN:$PATH
 
# setup-network-environment
if [ -f /etc/network-environment ]; then
    tnef=`mktemp`
    cp -a /etc/network-environment ${tnef}
    sed --in-place 's~[^0-9A-Za-z\=\.\_/]\+~_~g' ${tnef}
    source ${tnef}
    export $(cut -d= -f1 ${tnef})
    rm -rf ${tnef}
fi
EOF

You should logout and log back in now.

setup-network-environment

Download, build, and install setup-network-environment:

go get github.com/kelseyhightower/setup-network-environment

Configure

systemd

If you need to refresh your memory on basic systemd commands, please see my systemd shortcuts snippet.

Service

Save the following contents to /etc/systemd/system/setup-network-environment.service

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[Unit]
Description=Setup Network Environment
Documentation=https://github.com/kelseyhightower/setup-network-environment
Requires=network.target
After=network.target
 
[Service]
ExecStart=/usr/local/bin/setup-network-environment
RemainAfterExit=yes
Type=oneshot
 
[Install]
WantedBy=multi-user.target

Create an environment variable to use for the next set of commands:

sysDserviceSaveFile=/etc/systemd/system/setup-network-environment.service

Run the following set of commands together, including the curly braces:

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{
 
if $? -eq 0; then echo "Working on ${sysDserviceSaveFile}"; else echo "Unknown variable"; exit; fi
 
# Set permissions
chmod -v 644 ${sysDserviceSaveFile}
 
# Reload management parameters
systemctl daemon-reload
 
# Enable system service
systemctl enable "${sysDserviceSaveFile}"
 
# Start system service
systemctl start "${sysDserviceSaveFile}"
 
# Check status
systemctl status "${sysDserviceSaveFile}"
 
}

View generated environment file:

cat /etc/network-environment

Example dependencies

In the next few pages, I’ll cover examples where setup-network-environment is used with other programs:

  1. Launching Nginx with Docker.
  2. Updating /etc/network-environment when a VPN connection is started and stopped.

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