How to update php on debian without breaking Bitrix24?

Question

PHP

It so happened that the Bitrix24 box was installed on Debian
Debian GNU/Linux 8
Distributor ID: Debian
Description: Debian GNU/Linux 8.8 (jessie)
Release: 8.8
Codename: jessie
PHP 5.6.30-0+deb8u1 (cli)
mysql
+--- ------------------+
| 5.5.55-0+deb8u1-log It is
necessary to upgrade to the latest version of PHP and Mysql without killing Bitrix24.
Has anyone come across a similar case? What are the pitfalls?
Something tells me that the safest way is to deploy a new server, raise Bitrix there and simply migrate there with all the data.
But the customer, alas, just wants to upgrade, "here and now."
I ask you to tell me with the direction of action, unfortunately I myself do not understand much in this matter.
If there was a similar experience, I will be glad to cooperate and delegate this task to an experienced specialist (if you work in white, of course) =)

Answer 1

If updating php, then the best way is to bring up a new PHP, then redirect the server (nginx or Apache) to the new version. Updating in this way should not cause the service to be unavailable. If we talk about the MySQL database, then it is best to set up replication (most likely master-master), then update the replicas in turn, remembering to change the connection settings to always work only with a live replica.
For convenience, you can use containers, but in the case of a database, you still have to set up replication, and putting a database in a container is not a good idea.

Answer 2

You can put it in parallel, but this is a bad way.
A good way is to start a container or virtual machine for each group of projects or even within the same project.

Answer 3

The Bitrix opinion is to raise the Bitrix web environment, move b24 there.
My opinion, nothing complicated, if there are nights and weekends, we update the deb to 9, and everything we need is by hand.
If there are no nights and weekends, then downtime will be noticed, work there for 3 hours for an experienced debian.