1
00:00:00,222 --> 00:00:01,574
‫Now that we've seen resources,

2
00:00:01,574 --> 00:00:02,887
‫the second most important one

3
00:00:02,887 --> 00:00:04,208
‫is going to be parameters.

4
00:00:04,208 --> 00:00:06,406
‫And parameters are a way to provide inputs

5
00:00:06,406 --> 00:00:08,635
‫to your AWS CloudFormation template.

6
00:00:08,635 --> 00:00:09,877
‫They're super important to know about

7
00:00:09,877 --> 00:00:11,438
‫if you want to reuse your templates across

8
00:00:11,438 --> 00:00:15,187
‫the company or other accounts or regions.

9
00:00:15,187 --> 00:00:18,659
‫And some inputs cannot be determined ahead of time.

10
00:00:18,659 --> 00:00:20,336
‫For example, the keep area you're going

11
00:00:20,336 --> 00:00:22,501
‫to link to instances.

12
00:00:22,501 --> 00:00:25,021
‫Parameters are very powerful, they can be controlled,

13
00:00:25,021 --> 00:00:26,782
‫and they can prevent errors down the line

14
00:00:26,782 --> 00:00:30,027
‫happening in your templates, thanks to types.

15
00:00:30,027 --> 00:00:32,654
‫So, we've used parameters before

16
00:00:32,654 --> 00:00:35,149
‫in the first hands on, in which we basically

17
00:00:35,149 --> 00:00:39,095
‫had to specify the security group description.

18
00:00:39,095 --> 00:00:41,121
‫So, it was a string and we were asked

19
00:00:41,121 --> 00:00:42,754
‫for the security group description,

20
00:00:42,754 --> 00:00:45,454
‫and that was used in the security group itself.

21
00:00:45,454 --> 00:00:47,923
‫So, you should use the parameter when basically

22
00:00:47,923 --> 00:00:49,164
‫you ask yourself the question,

23
00:00:49,164 --> 00:00:51,458
‫"Is this CloudFormation resource configuration

24
00:00:51,458 --> 00:00:53,123
‫"likely to change in the future?"

25
00:00:53,123 --> 00:00:54,904
‫If so, you can make it a parameter.

26
00:00:54,904 --> 00:00:56,496
‫And by doing it as a parameter,

27
00:00:56,496 --> 00:00:59,118
‫you don't have to re-upload a template to change content.

28
00:00:59,118 --> 00:01:01,663
‫It's a bit more stable and a bit modualized.

29
00:01:01,663 --> 00:01:03,272
‫If you do programming, and I hope you do,

30
00:01:03,272 --> 00:01:06,439
‫you know the advantages of parameters.

31
00:01:07,744 --> 00:01:09,727
‫Now, parameters can have different settings,

32
00:01:09,727 --> 00:01:11,644
‫and they can be controlled in many different ways.

33
00:01:11,644 --> 00:01:13,577
‫I don't think the exam requires you to know

34
00:01:13,577 --> 00:01:16,043
‫all of these but, for me, for your interest,

35
00:01:16,043 --> 00:01:17,560
‫I'm just going to name them.

36
00:01:17,560 --> 00:01:19,465
‫You can have a typing string, number,

37
00:01:19,465 --> 00:01:21,986
‫CommaDelimitedList, list of a type,

38
00:01:21,986 --> 00:01:23,845
‫and an AWS Parameter.

39
00:01:23,845 --> 00:01:26,205
‫As far as description, you can have constraints,

40
00:01:26,205 --> 00:01:27,830
‫you can have a ConstraintDescription,

41
00:01:27,830 --> 00:01:29,960
‫a minimum and a max length for string,

42
00:01:29,960 --> 00:01:32,055
‫a minimum and a max value for numbers,

43
00:01:32,055 --> 00:01:33,997
‫you can have defaults, AllowedValues

44
00:01:33,997 --> 00:01:36,194
‫when you want to restrict the number of values

45
00:01:36,194 --> 00:01:38,275
‫a user can pick, AllowedPattern when you want

46
00:01:38,275 --> 00:01:43,275
‫to verify the inputs of a user using irregular expression,

47
00:01:43,307 --> 00:01:47,535
‫and NoEcho if you want to pass in the secrets basically.

48
00:01:47,535 --> 00:01:49,725
‫So, this is a lot of different optimizations

49
00:01:49,725 --> 00:01:51,164
‫and parameters you can do.

50
00:01:51,164 --> 00:01:52,725
‫For now, the only thing we've done is

51
00:01:52,725 --> 00:01:55,438
‫use a simple string parameter in our thing,

52
00:01:55,438 --> 00:01:57,667
‫and that's all you should know I think for the exam.

53
00:01:57,667 --> 00:01:59,800
‫So, how do you reference a parameter?

54
00:01:59,800 --> 00:02:03,087
‫Well, like this you have to use the function called Ref.

55
00:02:03,087 --> 00:02:05,863
‫And so, this is the first time we encounter Ref

56
00:02:05,863 --> 00:02:08,496
‫and functions, but basically interesting functions

57
00:02:08,496 --> 00:02:11,647
‫in your templates allow you to supercharge it

58
00:02:11,647 --> 00:02:13,317
‫and to link things up.

59
00:02:13,317 --> 00:02:15,879
‫And so the Ref function is one of the most used,

60
00:02:15,879 --> 00:02:18,215
‫and so you use it to reference parameters,

61
00:02:18,215 --> 00:02:19,751
‫and this way you can use your parameters

62
00:02:19,751 --> 00:02:22,430
‫anywhere in your templates, so in your resources,

63
00:02:22,430 --> 00:02:27,320
‫for any type of inputs, and parameters, and configs.

64
00:02:27,320 --> 00:02:32,259
‫So, the shorthand for a reference function in the YAML

65
00:02:32,259 --> 00:02:35,317
‫is a little exclamation point Ref.

66
00:02:35,317 --> 00:02:38,433
‫And this is why, it's just a way for us to have

67
00:02:38,433 --> 00:02:40,973
‫a much nicer syntax, easier to recognize.

68
00:02:40,973 --> 00:02:43,695
‫You can use the FN column call in Ref as well,

69
00:02:43,695 --> 00:02:45,743
‫it's whatever you want, but most likely,

70
00:02:45,743 --> 00:02:50,150
‫it's going to be this exclamation point Ref for shorthand.

71
00:02:50,150 --> 00:02:52,465
‫And the function can also be used to reference

72
00:02:52,465 --> 00:02:54,163
‫other elements within a template.

73
00:02:54,163 --> 00:02:56,184
‫So, in the template we've been using,

74
00:02:56,184 --> 00:02:58,353
‫in the parameter section, we had to find

75
00:02:58,353 --> 00:03:01,429
‫a parameter name security group description.

76
00:03:01,429 --> 00:03:04,839
‫Turns out that if we look all the way down,

77
00:03:04,839 --> 00:03:07,107
‫the security group description was used

78
00:03:07,107 --> 00:03:10,139
‫in this security group description key,

79
00:03:10,139 --> 00:03:13,694
‫and so we used the Ref function to reference it.

80
00:03:13,694 --> 00:03:15,626
‫So, this Ref function basically says,

81
00:03:15,626 --> 00:03:18,977
‫"Whatever the user will put as a parameter value,

82
00:03:18,977 --> 00:03:22,670
‫"for this parameter key, you want to use this,

83
00:03:22,670 --> 00:03:25,076
‫"reference it into the group description."

84
00:03:25,076 --> 00:03:26,888
‫So, it's very simple to think about.

85
00:03:26,888 --> 00:03:28,190
‫It's just a reference.

86
00:03:28,190 --> 00:03:31,377
‫But this reference function can also be used somewhere else.

87
00:03:31,377 --> 00:03:33,377
‫It was used right here, for example,

88
00:03:33,377 --> 00:03:36,557
‫for security groups, so you can see this reference function

89
00:03:36,557 --> 00:03:39,107
‫also referenced the SSH security group

90
00:03:39,107 --> 00:03:41,447
‫that was created under Resources.

91
00:03:41,447 --> 00:03:45,046
‫So the Ref function can be used both to reference

92
00:03:45,046 --> 00:03:47,157
‫parameters like the one before,

93
00:03:47,157 --> 00:03:50,827
‫or it can also be used to reference resources.

94
00:03:50,827 --> 00:03:53,016
‫So, here we've referenced the two security groups

95
00:03:53,016 --> 00:03:57,274
‫and within the EIP, we reference MyInstance.

96
00:03:57,274 --> 00:03:59,283
‫So, as you can see, the name of the reference

97
00:03:59,283 --> 00:04:04,004
‫is the exact same name as the logical value under Resources.

98
00:04:04,004 --> 00:04:06,682
‫Finally, you have a concept of Pseudo Parameters,

99
00:04:06,682 --> 00:04:10,468
‫and these are AWS offer parameters that we can use,

100
00:04:10,468 --> 00:04:12,740
‫and anytime they're enable by default,

101
00:04:12,740 --> 00:04:14,376
‫and we get just a bunch of values

102
00:04:14,376 --> 00:04:15,636
‫you may want to retrieve.

103
00:04:15,636 --> 00:04:18,671
‫So, we can get an account ID, and you can just

104
00:04:18,671 --> 00:04:20,223
‫give us the value of the account ID,

105
00:04:20,223 --> 00:04:22,864
‫notification ARNs, no value if we don't want

106
00:04:22,864 --> 00:04:24,008
‫to return the value.

107
00:04:24,008 --> 00:04:26,202
‫We can also ask for the region in which

108
00:04:26,202 --> 00:04:29,767
‫our address CloudFormation template is being run at,

109
00:04:29,767 --> 00:04:31,366
‫so for example, US-east-2.

110
00:04:31,366 --> 00:04:33,808
‫We can also get a pseudo parameter for the Stack ID

111
00:04:33,808 --> 00:04:35,084
‫or the Stack name.

112
00:04:35,084 --> 00:04:37,487
‫Basically, you don't need to know about these too much,

113
00:04:37,487 --> 00:04:38,402
‫maybe the first one.

114
00:04:38,402 --> 00:04:40,342
‫Account idea's very important to get the value

115
00:04:40,342 --> 00:04:42,070
‫of the account ID if you were to try to construct

116
00:04:42,070 --> 00:04:46,348
‫some complicated ARN value in your CloudFormation template.

117
00:04:46,348 --> 00:04:48,230
‫But overall, you should just know that there is

118
00:04:48,230 --> 00:04:49,992
‫this concept of pseudo parameters,

119
00:04:49,992 --> 00:04:51,722
‫and again, you can use them at any time,

120
00:04:51,722 --> 00:04:54,877
‫just use a Ref, and you're all set.

121
00:04:54,877 --> 00:04:55,898
‫I hope that was helpful,

122
00:04:55,898 --> 00:04:57,106
‫I hope you know how they work now

123
00:04:57,106 --> 00:04:58,630
‫in your CloudFormation templates,

124
00:04:58,630 --> 00:04:59,673
‫and I will see you in the next lecture.