Q:

Package docker-ce is not available, but is referred to by another package. eoan 19.10

I've installed docker several times before on Ubuntu.  Not sure why this isn't working now.  There seems to be a release for eoan now.  My output is below.
joe@hpd:~$ sudo apt-get remove docker docker-engine docker.io containerd runc
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package 'docker-engine' is not installed, so not removed
Package 'containerd' is not installed, so not removed
Package 'docker' is not installed, so not removed
Package 'docker.io' is not installed, so not removed
Package 'runc' is not installed, so not removed
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
joe@hpd:~$ sudo apt-get update
Hit:1 http://prerelease.keybase.io/deb stable InRelease
Hit:2 https://updates.signal.org/desktop/apt xenial InRelease                                                                              
Hit:3 http://us.archive.ubuntu.com/ubuntu eoan InRelease                                                                                   
Hit:4 https://download.docker.com/linux/ubuntu eoan InRelease                                                                              
Get:5 http://us.archive.ubuntu.com/ubuntu eoan-updates InRelease [97.5 kB]                                                                 
Hit:6 http://packages.microsoft.com/repos/vscode stable InRelease                                                                          
Get:7 http://us.archive.ubuntu.com/ubuntu eoan-backports InRelease [88.8 kB]                                                               
Get:8 http://security.ubuntu.com/ubuntu eoan-security InRelease [97.5 kB]                                     
Hit:9 https://packages.microsoft.com/repos/azure-cli eoan InRelease                                                        
Hit:10 https://packages.microsoft.com/ubuntu/19.04/prod disco InRelease
Hit:11 https://packages.microsoft.com/repos/ms-teams stable InRelease
Fetched 284 kB in 1s (324 kB/s)
Reading package lists... Done
joe@hpd:~$ sudo apt-get install \
>     apt-transport-https \
>     ca-certificates \
>     curl \
>     gnupg-agent \
>     software-properties-common
Reading package lists... Done
Building dependency tree       
Reading state information... Done
ca-certificates is already the newest version (20190110).
curl is already the newest version (7.65.3-1ubuntu3).
software-properties-common is already the newest version (0.98.5).
apt-transport-https is already the newest version (1.9.4).
gnupg-agent is already the newest version (2.2.12-1ubuntu3).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
jgreenaw@hpd:~$ curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
OK
joe@hpd:~$ sudo apt-key fingerprint 0EBFCD88
pub   rsa4096 2017-02-22 [SCEA]
      9DC8 5822 9FC7 DD38 854A  E2D8 8D81 803C 0EBF CD88
uid           [ unknown] Docker Release (CE deb) <docker@docker.com>
sub   rsa4096 2017-02-22 [S]

joe@hpd:~$ sudo add-apt-repository \
>    "deb [arch=amd64] https://download.docker.com/linux/ubuntu \
>    $(lsb_release -cs) \
>    stable"
Hit:1 http://prerelease.keybase.io/deb stable InRelease
Hit:2 https://download.docker.com/linux/ubuntu eoan InRelease                                                                              
Hit:3 https://updates.signal.org/desktop/apt xenial InRelease                                                                              
Hit:4 http://us.archive.ubuntu.com/ubuntu eoan InRelease                                                                                   
Get:5 http://us.archive.ubuntu.com/ubuntu eoan-updates InRelease [97.5 kB]                                                                 
Hit:6 http://packages.microsoft.com/repos/vscode stable InRelease                                                                          
Get:7 http://us.archive.ubuntu.com/ubuntu eoan-backports InRelease [88.8 kB]                                                               
Get:8 http://security.ubuntu.com/ubuntu eoan-security InRelease [97.5 kB]                                      
Hit:9 https://packages.microsoft.com/repos/azure-cli eoan InRelease                                                        
Hit:10 https://packages.microsoft.com/ubuntu/19.04/prod disco InRelease
Hit:11 https://packages.microsoft.com/repos/ms-teams stable InRelease
Fetched 284 kB in 1s (330 kB/s)
Reading package lists... Done
jgreenaw@hpd:~$ sudo apt-get update
Hit:1 http://prerelease.keybase.io/deb stable InRelease
Hit:2 http://us.archive.ubuntu.com/ubuntu eoan InRelease                                                                                   
Hit:3 https://download.docker.com/linux/ubuntu eoan InRelease                                                                              
Get:4 http://us.archive.ubuntu.com/ubuntu eoan-updates InRelease [97.5 kB]                                                                 
Hit:5 https://updates.signal.org/desktop/apt xenial InRelease                                                                              
Get:6 http://us.archive.ubuntu.com/ubuntu eoan-backports InRelease [88.8 kB]                                                               
Hit:7 http://packages.microsoft.com/repos/vscode stable InRelease                                                        
Get:8 http://security.ubuntu.com/ubuntu eoan-security InRelease [97.5 kB]                                                
Hit:9 https://packages.microsoft.com/repos/azure-cli eoan InRelease                      
Hit:10 https://packages.microsoft.com/ubuntu/19.04/prod disco InRelease
Hit:11 https://packages.microsoft.com/repos/ms-teams stable InRelease
Fetched 284 kB in 1s (375 kB/s)
Reading package lists... Done
joe@hpd:~$ sudo apt-get install docker-ce docker-ce-cli containerd.io
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package docker-ce is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'docker-ce' has no installation candidate
E: Unable to locate package docker-ce-cli
E: Unable to locate package containerd.io
E: Couldn't find any package by glob 'containerd.io'
E: Couldn't find any package by regex 'containerd.io'

A:

First, In official documentation, there is no mention of eoan dist as of yet.
Second there is no stable version of docker available for eoan distribution as per my investigation (Distribution Repositories).
So here is what you can try:  
From Official Documentation:

Use the following command to set up the stable repository. To add the nightly or test repository, add the word nightly or test (or both) after the word stable in the commands below. Learn about nightly and test channels. 

Hence, use the nightly channel instead of stable
$ sudo add-apt-repository \
   "deb [arch=amd64] https://download.docker.com/linux/ubuntu \
   $(lsb_release -cs) \
   stable nightly"

Good Luck!

