What do you mean, can you give some examples ?

Sure, thats needs because this variable should be available in any place for this process, just because this code executes in context where works any output commands like write

I would recommend regexr.com and regex101.com as a tools for testing regular expressions, this tools a bit simpler, but works online and cost nothing.

You have two cases, you change storage definition or you can use calculated value. But in case with calculated value, you have two options. It's an object's access and sql access, and such getter it is just only for object's access. For SQL you should define SqlComputeCode. Something like this.

Property Invalid As %Library.Boolean [Calculated, SqlComputed, SqlComputeCode = { s {*}={+$G(^GLOBAL({Code},"INVALID"))} }];

more details in documentation

$zhex
hex to dec

write $zhex("99")
​153

and back, dec to hex

write $zhex(153)
​99

be careful, hexadecimal should be a string and decimal should be a number

There are no particular recommended SourceControl systems. Everything depends on your choice.

Some time ago, with versions cache less then 2016.2 and before Atelier was appeared, we could use nothing except Studio. And in this case to work with particular SourceControl we should write own addon for Studio as a wrapper for this SourceControl. You can find one as a good example here on github, which works with GIT

Now, when we have Atelier, we could forget about this part, and use lots of available plugins for different SourceControl systems.

BTW, I prefer git, but most of time used SVN at work, and git for my own projects.

Yes, because $system.OBJ.Load() started support UDL, only in 2016.2 version

It's a right way, but don't you think, that you forgot to save your changes ? something like this

w rtn.%Save()

or you can just use $system.OBJ.Load("les.mac") or $system.OBJ.Load("some.class.cls") in versions 2016.2+
if you have less version but not less then 2014.1, you can load class with %Compiler.UDL.TextServices  as I've already offered to use it for export on stackoverflow

As I'm not sure what you mean by 'dead' locks, I'll just show simple code for looking all locks in current namespace

    set lockName=""
    for {
        set lockName=$order(^$LOCK(lockName))
        quit:lockName=""
        set mode=^$LOCK(lockName,"MODE")
        set owner=^$LOCK(lockName,"OWNER")
        write !,mode,?4,owner,?12,lockName
    }

What do you mean by dead locks ?

Studio reformats some class parts, such as Methods defenitions when you save it.

But as I know feature Atelier, stores class definition as is, so you do not need more such option, just format class as you need, and it should keep so.

As I've already had some experience in such systems in production, and one of our projects, has similar architecture exclude docker, just on windows, some physical servers with ECP-Client + CSPGateway + Apache, and one HAPorxy server for all of this server. And in this case all this scheme is quite static, and adding new ECP-client means some manual works, on all levels. But with docker I expect, just call something like this command 

docker-compose scale ecp=10

and just get some new working instances, which just after gets their new web-clients

To work it as microservices and split CSPgateway and Cache instance as different containers, I need to have simple package just only with CSPGateway, but FieldTest versions does not contain it. But yes sure, I think it is good way too, and in this case I can have more WEB-containers then Cache does, if it would be needed.

Timur, you can look at my example at github which I wanted to use in to article about using docker but have not managed yet. In this example I have Dockerfile for ECP-client, which can be build for particular ECP-server. And with %Installer manifest possible to make backward data channel too, while we have already known about where our server placed, we can connect to him via %Net.RemoteConnect or something else and make new backward connection, the problem is in this case how to remove old ones. I played only on one machine. But in anyway, Ansible still could be useful, but in case to prepare servers to work in docker cluster,  which should be prepared before we could use docker-compose and so on. And My example also contains web-server (apache), to have an access to this new instance. What I wanted to do then is to use some load balancer, HAProxy or traefik (as recommended Luca), to get one point access to my application, and dynamically expandable, without any manual operations, except scaling.

Yes, such language extension is very useful, but there is one more feature less known, and unfortunately completely undocumented. Its structured system variables, some of them could me familiar it is: ^$JOB,  ^$LOCK, ^$GLOBAL and ^$ROUTINE. More information in documentation here. But not all knows that it is possible to make your own such global. You should create routine with name SSVN"global_name" in %SYS namespace, for example SSVNZA for ^$ZA global

and for example with this code below, you SET, GET, KILL any values in this global, and this global will contain individual data for every session, and it is possible to use $order or even $query for  such global

ROUTINE SSVNZA
#define global $na(^CacheTemp.ZA($select($isobject($get(%session)):%session.SessionId,1:$job)))

fullName(glob) {
    set global=$$$global
    for i=4:1:glob set global=$na(@global@(glob(i)))
    quit global
}
set(glob, value) public {
    set global=$$fullName(.glob)
    set @global=value
}
get(glob) public {
    set global=$$fullName(.glob)
    quit @global
}
kill(glob, zkill=0) public {
    set global=$$fullName(.glob)
    if zkill {
        zkill @global
    } else {
        kill @global
    }
}
order(glob, dir) public {
    set global=$$fullName(.glob)
    quit $order(@global, dir) 
}
query(glob, dir) public {
    set global=$$fullName(.glob)
    set result=$query(@global, dir)
    quit:result="" ""
    set newGlobal=$name(^$ZA)
    for i=$ql($$$global)+1:1:$ql(result) {
        set newGlobal=$name(@newGlobal@($qs(result,i)))
    }
    quit newGlobal 
}

But as I said before, as it is completely undocumented feature a bit difficult to get complete compatibility with ordinary globals. But it still could be useful, in other cases, like it used by InterSystems.

if $data(^$JOB($zparent))=0 write "Parent is gone"

Stefan had already answered, and you can find his answer here