[kjhosein]

I've been thru the CFN v TF question. We came up with a list of benefits of TF over CFN. (Yes, I know - one-sided, but we wanted to document the decision with a bit more substance than "oh it's just better")

  * Ability to separate data (variables/parameters) from configs.
  * Easier to read (well at least pre-YAML CFN). 
  * Allows comments in the code.
  * Version control changes (diffs) are easier to read.
  * Multi-Cloud support. Works against AWS, Google Compute, Azure, Docker, more.
  * Multi-provider in general: can provision resources across multiple different cloud providers at once.
  * Can write modules in TF that can be reused in multiple different configs.
  * Tracks state via a version-controllable data file.
  * 'terraform plan' is essentially a no-op mode to see what changes would occur without actual running or making changes.
  * Actively developed.

[solidsnack9000]

Cloud Formation has good support for use from Python, Ruby, Node and the JVM (with template generators, to help out). If you're writing JSON directly, yes, some of the points above -- the first four, and the seventh -- are an issue; but if you use Python you get all the benefits of it being "real code" and "just a library" (unlike Terraform).

[hamandcheese]

This is a situation where I think not being "real code" is a feature of terraform. You declaratively represent your infrastructure rather than generate it with real code.

[solidsnack9000]

Over time, I have come to view "declarative infrastructure" as unrealistic. It's right 90% of the time, but not 100% of the time -- kind of like using only CSS and HTML. One should use markup whenever possible; but not everything on a page is truly "declarative". Occasionally one needs to script an input field or a transition.

One example of this is scripting the handoff process that's part of a blue/green deploy. In practice you'll want to look at organization defined metrics. There are libraries to do this -- either internal to your organization, or provided by a metrics vendor -- and scripting the process looks like this:

    (1) Setup new environment.
    (2) Divert some traffic.
    (3) Check metrics.
    (4) If metrics are okay:
        (4.1) Post message internally (IRC/Slack).
        (4.2) Divert all traffic.
        (4.3) Set up timed task to tear down old environment (in a day, hour, &c.).
    (5) If metrics are okay:
        (5.1) Post message internally (IRC/Slack), maybe to different people.
        (5.2) Stop diverting traffic.
        (5.3) Tear down new environment.

A large part of the work here is declarative: (1) by itself is a big piece of it, and is fully declarative, as is the teardown in (4.3) and (5.3). However, the need for control flow in this and many other cases means that, without a library, one must drive Terraform by templating and shelling out. Not being "real code" pushes one in the direction, not of greater declarativeness (libraries can certainly have declarative interfaces, like Troposphere does), but of worse code.

Many complex and powerful features are exposed to a modern business through libraries -- AI, payments, telephony -- and software defined infrastructure can be, too. The benefits of "infrastructure as code" won't be realized until that happens.

[tjbiddle]

A note on the Multi-Cloud support; OP is correct, it's not "switch to another provider" type setup - that's not where the power lies, the cool stuff is about being able to share attributes across clouds - Think about creating an AWS ELB, and then adding that CNAME entry into your CloudFlare account.

It also makes it for when/if you want to switch or start supporting other providers - your tool is already agnostic, and you don't need to go from CloudFormation and port over - you're already there.

[macmizer]

I have seen similar comments about "what happens if you want to switch providers" or "don't want to put all your eggs in one basket'. I can understand the comments but at the same time I do a lot of enterprise migrations with companies. We do not go in there while working through a plan on how to migrate to AWS or Google cloud and start promoting the multi provider feature of terraform. Why would you be going through so much effort to plan and move an entire enterprise into the cloud and use terraform and then throw in the idea that "Hey, you can also write the code to stand up similar services in another provider?" Maybe for smaller projects it would be attractive but for the big boys I don't see that to be very beneficial. At least this ability would not sway me to use Terra over CFT.