Hey everyone Can anyone help me out with a simple problem I Pulumi Community #aws

Hey everyone, Can anyone help me out with a simpl...

jolly-activity-81321

09/04/2023, 7:44 AM

Hey everyone, Can anyone help me out with a simple problem? I'd like to convert

pulumi.StringOutput

(EC2 instance public IP) to native string in Go. I was trying with

pulumi.Sprintf()

or with

pulumi.ApplyT()

with no success:

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stringValue := pulumi.String("Hello, World!").ToStringOutput()

fmt.Printf("%s", stringValue.ApplyT(func(s string) string {
		return s
}))

melodic-tomato-39005

09/04/2023, 8:48 AM

Hi Martins,

Apply

is the correct approach, but the

Printf

needs to be inside the callback function. See the example and explanation here.

jolly-activity-81321

09/04/2023, 9:19 AM

Hey Thomas

jolly-activity-81321

09/04/2023, 9:19 AM

I tried with

All

, same thing, basically

jolly-activity-81321

09/04/2023, 9:20 AM

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stringValue := pulumi.String("Hello, World!").ToStringOutput()
	fmt.Println(pulumi.All(stringValue).ApplyT(func(args []interface{}) (string, error) {
		s := args[0]
		return fmt.Sprintf("%v", s), nil
	}).(pulumi.StringOutput))

//Outputs {0xc00047a460}

jolly-activity-81321

09/04/2023, 9:20 AM

Outputs

{0xc00047a460}

where I expected

"Hello, World!"

melodic-tomato-39005

09/04/2023, 9:28 AM

You have two print statements here. The inner one should work, no? The outer one cannot work because

Apply

returns again an

Output

melodic-tomato-39005

09/04/2023, 9:29 AM

Also, using

All

is unnecessarily cumbersome if you have only one value,

ApplyT

is easier.

jolly-activity-81321

09/04/2023, 9:29 AM

I had it in the initial example, you said I needed

All

🙂

jolly-activity-81321

09/04/2023, 9:29 AM

ok, so

melodic-tomato-39005

09/04/2023, 9:30 AM

Hi Martins,
Apply
is the correct approach

jolly-activity-81321

09/04/2023, 9:35 AM

hmm

jolly-activity-81321

09/04/2023, 9:35 AM

so again, tried this:

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stringValue := pulumi.String("Hello, World!").ToStringOutput()
	original := stringValue.ApplyT(func(s string) (string, error) {
		return fmt.Sprintf("%v", s), nil
	})
	fmt.Printf("the parsed string is: %s", original)

jolly-activity-81321

09/04/2023, 9:36 AM

I mean, there should be super-simple way...

melodic-tomato-39005

09/04/2023, 9:46 AM

I suggest you give these docs another read. They have more examples, too. There’s a reason you can only access the string inside

Apply

, it’s how Pulumi’s whole model of tracking dependencies works.

melodic-tomato-39005

09/04/2023, 9:47 AM

Also note that there’s

Export

for when you want to use a value outside of your Pulumi program, or in another one

melodic-tomato-39005

09/04/2023, 9:48 AM

https://www.pulumi.com/learn/building-with-pulumi/stack-outputs/

jolly-activity-81321

09/04/2023, 1:36 PM

I've read this multiple times: https://www.pulumi.com/docs/concepts/inputs-outputs/#outputs-and-strings

jolly-activity-81321

09/04/2023, 1:37 PM

which suggests that using

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s := pulumi.Sprintf("%s", stringValue)

would work and give me a meaningful value... it does not...

jolly-activity-81321

09/04/2023, 1:43 PM

Export

is for exporting the value for use in a different stack, isn't it?

jolly-activity-81321

09/04/2023, 1:43 PM

I'm working in the same stack.

melodic-tomato-39005

09/04/2023, 1:46 PM

pulumi.Sprintf

is a helper wrapping

pulumi.Apply

. I think your examples above used

fmt.Sprintf

, which is different. But yes,

pulumi.Sprintf

with an argument of type

pulumi.StringOutput

should work.

jolly-activity-81321

09/04/2023, 1:47 PM

Copy code

stringValue := pulumi.String("Hello, World!").ToStringOutput()
	s := pulumi.Sprintf("%s", stringValue)
	fmt.Println(s)

jolly-activity-81321

09/04/2023, 1:48 PM

the output is

Copy code

{0xc0001a82a0}

jolly-activity-81321

09/04/2023, 1:48 PM

😢

melodic-tomato-39005

09/04/2023, 1:50 PM

Oh, I see. Well,

is again a

StringOutput

, not a

string

. Basically, the raw value wrapped by an Output cannot escape

Apply

and friends. Your logic working with the raw values needs to live in the callbacks to `Apply`/`All`/etc.

melodic-tomato-39005

09/04/2023, 1:50 PM

that’s this section:

If you need to access an output’s plain value—for example, to compute a derived, new value, or because you want to log it—you have these options:

• Apply: a callback that receives the plain value, and computes a new output

• Lifting: directly read properties off an output value

• Interpolation: concatenate string outputs with other strings directly

jolly-activity-81321

09/04/2023, 2:33 PM

Yeah, could be. But then again - why even bothering making those helper functions under

printf.go

from Pulumi's PoW?

jolly-activity-81321

09/04/2023, 2:34 PM

hell, my program is reduced to minimum, nothing working 😄

jolly-activity-81321

09/04/2023, 2:34 PM

Copy code

func main() {
	stringValue := pulumi.String("Hello, World!").ToStringOutput()
	s := pulumi.Sprintf("%s", stringValue)
	fmt.Println(s)
}

melodic-tomato-39005

09/04/2023, 2:37 PM

That’s not expected to work.

is a StringOutput, not a string, so you can’t print it. The print needs to happen inside an

Apply

, i.e., in the `Apply`’s callback. Like in the example in the docs:

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myPet.ID().ApplyT(func(id string) error {
    fmt.Printf("Hello, %s!", id)
	return nil
})

melodic-tomato-39005

09/04/2023, 2:38 PM

similar to the nodejs promise/callback model.

jolly-activity-81321

09/04/2023, 2:42 PM

Thanks Thomas for your patience 🙂

jolly-activity-81321

09/04/2023, 2:42 PM

I think I just have to wrap my head around it once again

melodic-tomato-39005

09/04/2023, 2:44 PM

No problem at all. The input/output model feels different to a lot of people. It helps if you’re worked with promises and callbacks but it’s not required.

jolly-activity-81321

09/04/2023, 3:06 PM

@melodic-tomato-39005 I think I found a way

jolly-activity-81321

09/04/2023, 3:07 PM

ctx.Export("publicIp", instance.PublicIp)

to export the value. I am provisioning EC2 instances in this case. 2. And then you can access it after running `Up`:

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upRes, err := stack.Up(ctx, stdoutStreamer)
	if err != nil {
		log.Fatal(err)
	}

	master.publicIp = fmt.Sprintf("%s", upRes.Outputs["publicIp"].Value)

jolly-activity-81321

09/04/2023, 3:08 PM

I'm getting my string value now, yay 🎉

melodic-tomato-39005

09/04/2023, 7:28 PM

Yep, that would be the way to access your string outside of your Pulumi stack. Either in another stack, or just in another non-Pulumi program. In one Pulumi program with one stack, though, that’s unnecessary. The string value is accessible inside the

Apply

/`All` callback functions.

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