If you've been in the tech industry for longer than 7 years, chances are good you've lived through some paradigm change in how things work. I've been here since 1996, so I've seen a few. And I'm looking down the barrel of another one. So I figured I would go over the renewal cycles I've personally lived through.
Ordered by dates impacting my career.
The Rise and Fall of Novell NetWare (Predates me, until about 2007)
Office automation was Novell NetWare for years. It was the first server in most offices, until they were replaced by either Windows NT, Windows 2000, or Windows 2003 machines. It was honestly the first distributed platform I ever worked with, since Novell Directory Services was a distributed database. It doesn't qualify as 'distributed' under today's definition, but in 1996 when NetWare 4.0 came out? It was cutting edge.
It was a NetWare migration that got me into Systems Administration in the first place. I did all the Sysadminny stuff like backups, user migrations, server patching and updates, and server consolidations. Servers were well pampered pets with cutesy names.
For me, NetWare died when my dayjob decided to get rid of it. I'm not at all surprised at the choice in retrospect. The upgrade at the time was from NetWare 6.5 (Novell kernel, 32-bit) to Open Enterprise Server (Linux kernel, 64-bit), and the effort to upgrade to that versus migrating everyone to Windows was equal enough we went to Windows instead.
Fun fact for newcomers: This very blog was hosted on NetWare for the first few years of its existence! It ran Apache! And Tomcat! Have a flash-back to that time.
This was the first operating system to die underneath me.
The Rise and Fall of File-Servers (Predates me through 2011)
File-serving is what NetWare did. The Windows migrations done were all to replace that functionality, and the NetWare admins involved were pissed because it was a step back in functionality. In my opinion, Windows didn't catch up to the NetWare feature-set until Server 2008.
But by 2008, the dedicated file-server was on the decline. At first it was NetApps, dedicated NAS systems.
Then it was things like SharePoint, that moved storage off of the direct-mapped file-share to application-specific application shares.
The university I was working for was one of the last market-segments to still operate large, clustered file-servers. When I left the university, it was in part because my dayjob had me working on a dead technology as a majority thing I was working on.
I'm not familiar with any new deployments of true file-servers. The orgs running them all started running them during the file-server era and haven't gotten rid of them yet.
The Rise and Fall of Actual Datacenters (Predates me to 2015)
The cloud mostly won. You need to be a certain size of company to make the physical plant of a datacenter make sense financially. Rack-n-stack sysadmins like me have moved on to cloudier things.
The Rise and Fall of Microsoft Windows (1997 through 2013)
I picked up Windows concurrent with NetWare, and grew my fluency with both at about the same rate. That made me marketable, which was nice. In the beginning (1997 through 2003) servers were still pampered pets with cutesy names. Once I moved to the university, the cutesy names mostly went away since our fleet was big enough we couldn't keep track of what Oberon did, but could figure out what AD-DC-3 did (2003-2011).
Then I moved to a startup that was using Windows as part of a SaaS product. That was an interesting time, but I learned lots doing it (2011-2013). By that time, servers were mere VMs with auto-generated names.
It stopped being relevant to my career in 2013, but I do have a soft spot for Windows.
The Rise and Fall of VMWare (2008 through 2015)
This was a big sea-change in how IT systems were managed. Once the Intel ISA support was there, ESX changed everything in IT. At the university I was working at, the rack with the ESX servers in it ate a sizable portion of the power-budget for the entire computer-room, at a fraction of the space that power-budget took in 2003. It was amazing.
Used it again at my first startup to manage an internal cloud of machines.
The big-corp after that was all ESX again with whole datacenters and a Managed Services platform on it. As I was leaving they were in the process of a lift-and-shift to AWS so they could close down their datacenter colos.
My current job does nothing with it because we have no physical datacenters.
The Rise of Linux (2011 to current)
I've been a Linux user since 1995, but wasn't allowed to administer it professionally until I moved to my first startup. This was one of several reasons why I left the University, by the way. I'm not going to spend much text on it, because Linux is central to so many things right now.
The Rise of Amazon AWS (2011 to current)
Using someone else's computers to do things! This was like VMware, but you didn't have to manage datacenters, or hardware, or power budgets, or rack-space, or cooling density, or cable-lengths, or server warranties, or out-of-band networks, or...
You paid someone else to handle all that, so you could focus on what you needed to focus on, which was provisioning operating systems and applications. And maybe not even that, if you end up using the managed-services like Relational Database Services, or go 'serverless' with Lambdas, ECS, and other techniques.
The Rise and Fall of VM-Oriented Configuration Management Systems (2011 through 2020)
Puppet was the first big-bang application in this space (there were others before it, like cfengine), with follow-ups in Chef, Salt, and Ansible. But Puppet was where I started, and still am. I spend a big chunk of my day making changes to our puppet-configs in order to bring change to what's running on our stuff. Infrastructure as code!
But Docker.
Puppet/Chef and company were all about building a VM image, or maintaining a pre-defined config on a running box. It does a great job of that, and auditors understand it. This paradigm doesn't work in Docker, which uses overlays to achieve similar things to how Puppet used modules. It sure can produce a VM-sized Docker image. But that image is not stylish.
The future has Puppet relegated to managing the state-maintaining systems that don't Docker well, and can't be run by your Cloud provider for some reason (be it compliance restrictions or technical).
From NetWare on a cutely named server in a closet, to a completely unnamed Docker instance in the Cloud, my career has been through a few paradigm changes. Change is constant. Just when I feel like I really know something well, a new thing comes along and I start anew.