install php7.4 on ubuntu 16.04 - Dockerfile

I am trying to install php7.4 and related packages with below commands

FROM ubuntu:16.04
RUN apt update \
    && apt install -y software-properties-common\
    && add-apt-repository ppa:ondrej/php \
    && apt-get update \
    && apt-get install -y php7.4

I get the below message

Reading package lists...
Building dependency tree...
Reading state information...
E: Unable to locate package php7.4
E: Couldn't find any package by glob 'php7.4'
E: Couldn't find any package by regex 'php7.4'

on searching with

apt-cache search php7

I see that only 7.0 related packages are available

php7.0 - server-side, HTML-embedded scripting language (metapackage)
php7.0-cgi - server-side, HTML-embedded scripting language (CGI binary)
php7.0-cli - command-line interpreter for the PHP scripting language
php7.0-common - documentation, examples and common module for PHP
php7.0-curl - CURL module for PHP

I am confused why I am not getting the newer versions as 7.3, 7,4 and 8 should be the only ones available today. How can I get php7.4 packages?

Solution

TL;DR: Since Ubuntu 16.04 reached "End of Standard Support", packages for it were removed from the PPA.

You might want to read this: https://github.com/oerdnj/deb.sury.org/issues/1567

In April 2021, Ubuntu 16.04 Xenial will reach End of Standard Support and will be available only as a paid option through Ubuntu Extended Security Maintenance.

What does it mean for DEB.SURY.ORG PPAs?

The packages for Ubuntu 16.04 will be deleted shortly after the EoL/EoSS is announced, usually at the same time as the next PHP release is published because it's not possible to build the packages any more.

The packages for Ubuntu 16.04 will be available via PHP LTS by Freexian paid program. This is cheaper option than previously announced Private dedicated repositories.