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Lab description

In this lab we learn about functions in Terraform.

Expressions

Setup

Make sure you are in the correct folder:

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cd ~/terraform-labs

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cd ~/terraform-labs

If you were unable to complete the last lab, you can find a copy of the files in the solutions folder

1. Launch Interactive Console

Terraform comes with an interactive console that is very handy to evaluate expresssions and exploring functions.

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terraform console

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terraform console

You should see your prompt > appear.

To exit the console at any time and go back to cloud shell’s terminal, just type exit or press ctrl + c. To clear the screen, press ctrl + l

NOTE: The Terraform console can be tricky to paste into. Right-click your mouse after copying an individual command to get it to work.

1. Explore and practice a handful of built-in functions using the console

Built-in functions greatly help with writing cleaner code. We will use some of the functions in our config later as well.

  1. Numeric Functions

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     # max value
 max(5,12,9)
    
 # max value from a list
 max([12,54,3]...)
    
 # ceil to return closest whole number that is greater than or equal to given value
 ceil(5.3)
    
 # parseint - parse a string as int for given base (decimal here)
 parseint("35", 10)

  2. String Functions

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     # split string into a list
 split(",", "foo,bar,baz")
    
 # convert list to a string based on a separator
 join(" ", ["foo", "bar", "baz"])
    
 # convert string to lower-case
 lower("HELLO")

  3. Collection Functions

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     # retrieve keys from a map as a list
 keys({a=1, c=2, d=3})
    
 # sort a list
 sort(["e", "d", "a"])
    
 # get length of string, list or map
 length([1, 2, 3, 4, 5])

  4. Type Conversion functions

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     # convert list to a set to remove duplicates 
 toset(["c", "b", "b"])

  5. Encoding Functions

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     # decode a base64 encoded string
 base64decode("SGVsbG8gV29ybGQ=")
    
 # encode given value as a json string
 jsonencode({"hello"="world"})

  6. Hash and Crypto Functions

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     # compute sha256 for given string
 sha256("hello world")

  7. Filesystem functions

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     # get absolute path of given filesystem path
 abspath(path.root)
    
 # read file contents and return them as a string
 file("main.tf")

  8. Date and time functions

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     # timeadd(timestamp, duration)
 timeadd("2020-06-08T00:00:00Z", "10m")

  9. IP Network functions

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     # calculate a subnet address within given IP network address prefix.
 # cidrsubnet(prefix, newbits, netnum)
 cidrsubnet("172.16.0.0/16", 8, 0)

2. Use the console to see Terraform settings

  1. Update main.tf include this locals block:

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     locals {
   subnets = cidrsubnets("10.0.0.0/24", 8, 7)
 }

  2. Exit the console with ctrl + c and then run terraform console again.

  3. Now you can access the values of the locals block:

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     local.subnets

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     local.subnets

For a full list of built-in functions, see below and try out the ones that you find interesting.

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