feat: drop support for unsupported Debian and Ubuntu releases

While the latest packages may continue to work on other releases, we will no longer officially support these releases, nor will we distribute packages.

docs/getting-started/install/debian.md

@@ -12,8 +12,8 @@ wget -nv -O - https://get.docker.com/ | sh
 
 # install dokku
 wget -nv -O - https://packagecloud.io/dokku/dokku/gpgkey | apt-key add -
-OS_ID="$(lsb_release -cs 2>/dev/null || echo "trusty")"
-echo "trusty utopic vivid wily xenial yakkety zesty artful bionic" | grep -q "$OS_ID" || OS_ID="trusty"
+OS_ID="$(lsb_release -cs 2>/dev/null || echo "bionic")"
+echo "xenial bionic" | grep -q "$OS_ID" || OS_ID="bionic"
 echo "deb https://packagecloud.io/dokku/dokku/ubuntu/ ${OS_ID} main" | sudo tee /etc/apt/sources.list.d/dokku.list
 sudo apt-get update -qq >/dev/null
 sudo apt-get install -qq -y dokku

docs/getting-started/install/digitalocean.md

@@ -6,7 +6,7 @@
 
 1. Login to your [DigitalOcean](https://m.do.co/c/fe06b043a083) account.
 2. Click **Create a Droplet**.
-3. Under **Choose an image > One-click apps**, choose the latest **Dokku** release for 16.04 _(version numbers may vary)_.
+3. Under **Choose an image > One-click apps**, choose the latest **Dokku** release for 18.04 _(version numbers may vary)_.
 4. Under **Choose a size**, select your machine spec.
 5. Under **Choose a datacenter region**, select your region.
 6. Add an SSH Key.

docs/getting-started/install/dreamhost.md

@@ -19,7 +19,7 @@ source openrc.sh # Set the environment variables for DreamHost Cloud
 
 This allows OpenStack client to connect to DreamHost API endpoints.
 The command below creates a new server instance named `my-dokku-instance`
-based on Ubuntu 14.04, with 2 GB RAM and 1 CPU (the flavor called
+based on Ubuntu 18.04, with 2 GB RAM and 1 CPU (the flavor called
 `supersonic`), opening network port access to HTTP and SSH (the
 `default` security group), and the name of the chosen SSH key. This
 key will be automatically added to the new server in the
@@ -28,7 +28,7 @@ be reused by Dokku.
 
 ```sh
 openstack server create \
-  --image Ubuntu-14.04 \
+  --image Ubuntu-18.04 \
   --flavor gp1.supersonic \
   --security-group default \
   --key-name $YOUR_SSH_KEYNAME \
@@ -46,7 +46,7 @@ server:
 apt_upgrade: true
 
 apt_sources:
- - source: "deb https://packagecloud.io/dokku/dokku/ubuntu/ trusty main"
+ - source: "deb https://packagecloud.io/dokku/dokku/ubuntu/ bionic main"
    key: |
     -----BEGIN PGP PUBLIC KEY BLOCK-----
     Version: SKS 1.1.5
@@ -107,7 +107,7 @@ apt_sources:
     =H60S
     -----END PGP PUBLIC KEY BLOCK-----
    filename: dokku.list
- - source: "deb https://apt.dockerproject.org/repo ubuntu-trusty main"
+ - source: "deb https://apt.dockerproject.org/repo ubuntu-bionic main"
    key: |
     -----BEGIN PGP PUBLIC KEY BLOCK-----
     Version: SKS 1.1.5

docs/getting-started/installation.md

@@ -6,7 +6,7 @@ Dokku is an extensible, open source Platform as a Service that runs on a single
 
 To start using Dokku, you'll need a system that meets the following minimum requirements:
 
-- A fresh installation of [Ubuntu x64 - Any currently supported release](https://www.ubuntu.com/download), [Debian 8.2 x64](https://www.debian.org/distrib/) or [CentOS 7 x64](https://www.centos.org/download/) *(experimental)* with the FQDN set <sup>[1]</sup>
+- A fresh installation of [Ubuntu 16.04/18.04 x64](https://www.ubuntu.com/download), [Debian 9 x64](https://www.debian.org/distrib/) or [CentOS 7 x64](https://www.centos.org/download/) *(experimental)* with the FQDN set <sup>[1]</sup>
 - At least 1 GB of system memory <sup>[2]</sup>
 
 You can *optionally* have a domain name pointed at the host's IP, though this is not necessary.
@@ -27,7 +27,7 @@ sudo DOKKU_TAG=v0.19.13 bash bootstrap.sh
 
 The installation process takes about 5-10 minutes, depending upon internet connection speed.
 
-If you're using Debian 8 or Ubuntu 14.04, make sure your package manager is configured to install a sufficiently recent version of nginx<sup>[3]</sup>, otherwise, the installation may fail due to `unmet dependencies` relating nginx.
+If you're using Debian 9 or Ubuntu 18.04, make sure your package manager is configured to install a sufficiently recent version of nginx<sup>[3]</sup>, otherwise, the installation may fail due to `unmet dependencies` relating nginx.
 
 #### 2. Setup SSH key and Virtualhost Settings
 

docs/getting-started/troubleshooting.md

@@ -198,7 +198,7 @@ __Symptom:__ I successfully deployed my application with no deployment errors bu
 
 __Solution:__
 
-This can occur if Dokku is running on a system with a firewall like UFW enabled (some OS versions like Ubuntu 16.04 have this enabled by default). You can check if this is your case by running the following script:
+This can occur if Dokku is running on a system with a firewall like UFW enabled (some OS versions like Ubuntu have this enabled by default). You can check if this is your case by running the following script:
 
 ```shell
 sudo ufw status