Select default emulator on first run by anisaoshafi · Pull Request #217 · localstack/lstk

anisaoshafi · 2026-04-30T15:02:43Z

First-time users are prompted to choose their emulator (AWS or Snowflake) before lstk starts (to simulate this, rename or delete config.toml). The choice is saved to the config file immediately.

When run with --non-interactive / no TTY it silently uses the AWS by default.

Note to user they can change to the other emulator:

carole-lavillonniere · 2026-05-05T08:27:48Z

@anisaoshafi @gtsiolis it feels a bit odd to me that the --emulator flag overwrites the config. The convention for flags as far as I know is to be transient/ephemeral.

Users can still manually edit their config if they want to.

If we want to provide a way to reset the emulator in the config from command line, what about something like lstk start --reset-config or lstk config emulator that would prompt again Which emulator would you like to use?

lstk start --emulator <type> could override the config, but only temporarily.

anisaoshafi · 2026-05-05T08:33:30Z

@anisaoshafi @gtsiolis it feels a bit odd to me that the --emulator flag overwrites the config. The convention for flags as far as I know is to be transient/ephemeral.

Users can still manually edit their config if they want to.

If we want to provide a way to reset the emulator in the config from command line, what about something like lstk start --reset-config or lstk config emulator that would prompt again Which emulator would you like to use?

lstk start --emulator <type> could override the config, but only temporarily.

Good point, can be too much of a responsibility for a flag.

I like lstk config emulator option. Does the same but in a more controlled way since the user have to confirm the option, or cancel if that's not what they intended.
Will wait for @gtsiolis's opinion before making the changes 🙏🏼

carole-lavillonniere · 2026-05-05T08:44:37Z

@anisaoshafi @gtsiolis it feels a bit odd to me that the --emulator flag overwrites the config. The convention for flags as far as I know is to be transient/ephemeral.
Users can still manually edit their config if they want to.
If we want to provide a way to reset the emulator in the config from command line, what about something like lstk start --reset-config or lstk config emulator that would prompt again Which emulator would you like to use?
lstk start --emulator <type> could override the config, but only temporarily.

Good point, can be too much of a responsibility for a flag.

I like lstk config emulator option. Does the same but in a more controlled way since the user have to confirm the option, or cancel if that's not what they intended. Will wait for @gtsiolis's opinion before making the changes 🙏🏼

If we decide for another command, I think we can leave it out of the scope of this PR/create another issue for it to keep this PR small.

carole-lavillonniere · 2026-05-05T07:51:25Z

+tag  = "latest"
+port = "4566"
+# volume = ""    # Host directory for persistent state (default: OS cache dir)
+# env = []       # Named environment profiles to apply (see [env.*] sections below)`


question:
At the moment those blocks are duplicated and there is a chance of drift.
How hard it is to parse those blocks from default_config.toml?
Another solution could be to use go templates in default_config.toml so the container blocks could come from another file.

Addressed here 🙏🏼 0aeca91

gtsiolis · 2026-05-05T12:22:33Z

Looking at this now! 👀

gtsiolis · 2026-05-05T12:57:20Z

+type = "snowflake"
+tag  = "latest"
+port = "4566"


issue: Similar to what @carole-lavillonniere mentioned above, this leads to content duplication.

# [[containers]] # type = "aws" # Emulator type. Currently supported: "aws", "snowflake" # tag = "latest" # Docker image tag, e.g. "latest", "2026.03" # port = "4566" # Host port the emulator will be accessible on # # volume = "" # Host directory for persistent state (default: OS cache dir) # # env = [] # Named environment profiles to apply (see [env.*] sections below) [...] [[containers]] type = "snowflake" tag = "latest" port = "4566" # volume = "" # Host directory for persistent state (default: OS cache dir) # env = [] # Named environment profiles to apply (see [env.*] sections below)

I'd expect if I select SNO on start, to simply use snowflake in the first [[containers]] section.

[...] [[containers]] type = "snowflake" # Emulator type. Currently supported: "aws", "snowflake" tag = "latest" # Docker image tag, e.g. "latest", "2026.03" port = "4566" # Host port the emulator will be accessible on volume = "" # Host directory for persistent state (default: OS cache dir) env = [] # Named environment profiles to apply (see [env.*] sections below) [...]

I'm going to tackle this 💯

Addressed here 🙏🏼 0aeca91

gtsiolis · 2026-05-05T14:52:40Z

+		Prompt: "Which emulator would you like to use?",
+		Options: []output.InputOption{
+			{Key: "a", Label: "AWS [A]"},
+			{Key: "s", Label: "Snowflake [S]"},


issue(non-blocking): Here's what most users with no access to SNO emulation will see. I guess this comes from the emulator, right? Could we mask now or later this error?

SNO users in trial see no error currently.

Have to check what SNO-only users in production see.

yes, comes from emulator side. I created a follow up task: DRG-818 for handling this error in a nicer way since it's out of the scope for this PR 🙏🏼

gtsiolis · 2026-05-05T14:55:48Z

+
+	msg := selected.DisplayName() + " emulator selected."
+	if configPath != "" {
+		msg += fmt.Sprintf(" You can change this anytime in %s.", configPath)


issue: The message here wraps early on line 2, can we make the message wrap normally in two lines, I think we do so for other messages, right?

@gtsiolis Does this look a bit better? Also changed the message as you proposed in the other comment

What do you think of using the same success message as the AWS profile creation? This will avoid ending up with multiple NOTE messages when the emulator is running (although edge case) and make the output more functional upon selection.

1/2 2/2

same success message as the AWS profile creation

What does this mean when the user selects snowflake on first try?

@gtsiolis sorry, I'm not following. Can you rephrase your suggestion?
Did you mean Change configuration in ~/.config/lstk/config.toml should have a green tick in front?

gtsiolis · 2026-05-05T14:57:39Z

+	labelCh <- label
+}
+
+func selectEmulatorInTUI(


praise: Thanks for reusing this UX!

carole-lavillonniere · 2026-05-07T06:52:13Z

+
+	return newCfg.Containers, nil
+}
+


issue: now I think we should just move selectEmulatorInTUI and resolveAndCacheLabel out of internal/ui and we should be good. These are domain code.

AGENTS.md is kind of documenting this with:

Do not pass UI callbacks like onProgress func(...) through domain layers; prefer typed output events.

Keep UI as presentation/orchestration only; business logic stays in domain packages.

domain packages => everything under internal/ except internal/ui/.
A test for "is this domain code?": if we wired a different kind of frontend, domain code should still work.

AGENTS.md does not explicitly say where the code executed upon user input lives, though. I think it'd be good to add a line about this.

Attempted to address here: fe93529

carole-lavillonniere · 2026-05-07T06:58:42Z

+		return name
+	}
+	return string(e)
+}


question: we already have DisplayNameForType line 77.
Can we

refactor to make them one?

or rename to make more explicit?

and/or change the signatures so that they are both methods?

Tried here: 62926ca

carole-lavillonniere · 2026-05-07T07:00:40Z

+		Prompt: "Which emulator would you like to use?",
+		Options: []output.InputOption{
+			{Key: "a", Label: "AWS"},
+			{Key: "s", Label: "Snowflake"},


nit: possible to build the options from emulatorDisplayNames or another map, to make it more dynamic?

Tried here: b4fc4cf

carole-lavillonniere · 2026-05-07T07:03:06Z

+		}
+		*firstRun, err = config.Init()
+		return err
+	}


question: do we really need 2 functions initConfig and initConfigCapturingFirstRun? They look quite similar

Good point, tried here: 6ced3fe

carole-lavillonniere · 2026-05-07T07:12:58Z

+
+	cancel()
+	<-outputCh
+}


suggestion: what about completing this test with an actual user input, making sure we persist the choice in the config and start that chosen emulator?

suggestion: we could also add a simple test to make sure we don't prompt when the config is already created?

Good point: tried here and here 🙏🏼

…ckType

…ation message is secondary

carole-lavillonniere

🥳

anisaoshafi added the semver: patch label Apr 30, 2026

anisaoshafi force-pushed the drg-381-add-option-to-select-default-emulator branch 17 times, most recently from e1db26a to 4204284 Compare May 4, 2026 15:34

anisaoshafi marked this pull request as ready for review May 4, 2026 15:39

anisaoshafi requested review from carole-lavillonniere and silv-io as code owners May 4, 2026 15:39

anisaoshafi requested a review from gtsiolis May 4, 2026 15:39

carole-lavillonniere reviewed May 5, 2026

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anisaoshafi marked this pull request as draft May 5, 2026 11:24

anisaoshafi force-pushed the drg-381-add-option-to-select-default-emulator branch from ada0134 to 5e7723a Compare May 5, 2026 12:34

gtsiolis reviewed May 5, 2026

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anisaoshafi marked this pull request as ready for review May 6, 2026 12:00

anisaoshafi mentioned this pull request May 6, 2026

Improve error for users with no snowflake license #230

Merged

carole-lavillonniere reviewed May 7, 2026

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anisaoshafi added 22 commits May 7, 2026 13:07

Select default emulator on first run

0c17622

Parallelize new tests

d7fcdfb

Remove error & rename message for default emulator

ea7166a

Match single quotes in config & handle commented section in detectBlo…

d6713e3

…ckType

Assert error from runLstk

d2e8857

Move ParseEmulatorType to its domain package

796b7ae

Make switch_test.go tests table-driven

8b35fa3

Strong-type --emulator, validate early

b6dc825

Remove callback in startEmulator: handle in run.go

a18bb3b

Remove ParseEmulatorType in favor of ParseOptionalEmulatorType

ad2945f

Gentler message on changing configuration

b52e540

Avoid duplicating config content

b177aa7

Skip keyboard shortcuts for emulator selection

4afa6fc

Nits

49c7698

Split emulator-selected note into two message events: change configur…

31cb5b9

…ation message is secondary

Simplify: Remove --emulator flag on start

d651cd8

Move domain code to proper place

fe93529

Refactor display name related functions

62926ca

Reuse for emulator name

b4fc4cf

Get rid of initConfigCapturingFirstRun

6ced3fe

Enhance test by capturing user input & persisting in config

238b97a

New test: emulator selection not triggered when config exists

3d88700

anisaoshafi force-pushed the drg-381-add-option-to-select-default-emulator branch from f4d7f78 to 3d88700 Compare May 7, 2026 11:07

carole-lavillonniere approved these changes May 7, 2026

View reviewed changes

anisaoshafi merged commit bf72a00 into main May 7, 2026
12 checks passed

anisaoshafi deleted the drg-381-add-option-to-select-default-emulator branch May 7, 2026 11:26

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gtsiolis commented May 5, 2026

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anisaoshafi commented Apr 30, 2026 •

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