Update step-by-step send payment guide with docker

[Euler-B]

Change Description

This PR is the result of a step-by-step validation of the Send Payment Guide with Docker. After encountering several issues with the original workflow, I conducted a deep dive into the underlying failures, testing all available options described in the guide and researching related documentation.

The result is an updated, functional guide that works out-of-the-box. Key changes include:

• Simnet Focus: This update specifically focuses on Simnet due to its simplicity in block generation. It provides a seamless environment for new developers to test LND payment commands instantly without external dependencies.

• Removal of Obsolete Resources: I have removed the section regarding the faucet.lightning.community.web , as it is currently offline.

• Signet Considerations: I've clarified that obtaining funds via Signet can be time-consuming, as it depends on available computing power for mining/proof-of-work requirements, which might frustrate newcomers.

This guide now serves as a reliable and modern reference for anyone’s first encounter with the LND payment flow..

Steps to Test

Follow the instructions provided in the updated docker/README.md.

Pull Request Checklist

Testing

• Your PR passes all CI checks.
• Tests covering the positive and negative (error paths) are included.
• Bug fixes contain tests triggering the bug to prevent regressions.

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• The change is not insubstantial. Typo fixes are not accepted to fight bot spam.
• The change obeys the Code Documentation and Commenting guidelines, and lines wrap at 80.
• Commits follow the Ideal Git Commit Structure.
• Any new logging statements use an appropriate subsystem and logging level.
• Any new lncli commands have appropriate tags in the comments for the rpc in the proto file.
• There is a change description in the release notes, or [skip ci] in the commit message for small changes.

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[gemini-code-assist]

Summary of Changes

Hello @Euler-B, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request delivers a thoroughly validated and updated step-by-step guide for setting up and sending payments using LND with Docker. It resolves previous workflow issues, ensuring a reliable and out-of-the-box experience for users interacting with the LND payment flow. The changes encompass dependency updates, command syntax modernization, and configuration adjustments across the Docker environment for LND and BTCD.

Highlights

• docker/README.md Updates: The guide for sending payments with Docker has been significantly revised, including updated Docker prerequisites, modern docker compose command syntax, and the removal of an outdated "Connect to faucet lightning node" section.
• btcd Dockerfile Enhancements: The btcd Dockerfile now uses a newer Go version (1.25.3), updates the BTCD_VERSION to v0.24.2, specifies alpine:3.20 as the base image, corrects segnet to signet in comments, and includes a HEALTHCHECK for the btcd service.
• docker-compose.yml Modernization: The deprecated version: '2' declaration has been removed, and the btcd service build now explicitly references its Dockerfile.
• lnd Startup Script Adjustments: The start-lnd.sh script has been updated to remove the --$CHAIN.active flag, correctly specify the btcd RPC host with its port (:18555), and set the rpclisten address to 127.0.0.1:10009 for improved clarity and security within the Docker environment.

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[gemini-code-assist]

Code Review

This pull request provides a welcome update to the Docker-based lnd payment guide. Key improvements include updating to the docker compose v2 syntax, removing an outdated section, and upgrading dependencies. The Dockerfiles are also enhanced with better version management and a health check.

However, I've identified a critical error in docker/lnd/start-lnd.sh. The script configures lnd to use the wrong port for the btcd RPC connection on simnet, which will prevent the setup from working as described. I've provided specific comments with suggestions to resolve this.

[gemini-code-assist]

The btcd RPC host is being configured with port 18555, which is the P2P port for simnet, not the RPC port. The correct RPC port for btcd on simnet is 18556. This configuration will prevent lnd from connecting to btcd and should be corrected.

Suggested change

	"--$BACKEND.rpchost"="$RPCHOST:18555" \
	"--$BACKEND.rpchost"="$RPCHOST:18556" \

[gemini-code-assist]

This comment incorrectly states that 18555 is the default btcd RPC port for simnet. The correct default RPC port for btcd on simnet is 18556. Port 18555 is the P2P port. This is misleading and should be corrected to avoid confusion, especially as the incorrect port is used later in this script.

Suggested change

	# [:18555] is the default btcd RPC port in SIMNET network.
	# [:18556] is the default btcd RPC port in SIMNET network.

[Liongrass]

Hi! Thank you for that PR!
My initial question is, is this guide for Signet or Simnet? Right now it makes references to both. Can you also double-check if the BTCD ports are correct?

[Euler-B]

Hi! Thank you for that PR! My initial question is, is this guide for Signet or Simnet? Right now it makes references to both. Can you also double-check if the BTCD ports are correct?

Hi! Thanks for the review. Sorry for the confusion; here are the details:

The guide is intended to use Simnet, as it's the fastest way to test the payment flows locally.

The Simnet ports are correct. Regarding Signet, I verified them while testing the faucet part, but I noticed a typo ("Segnet" instead of "Signet") which I've now fixed.

Regarding your question about the Dockerfile: I believe it's best to keep the Simnet focus to ensure the fastest onboarding for developers. I will refine the documentation to make this distinction clear and remove any ambiguous references to Signet where they aren't needed.

I've just updated the PR with these corrections. Let me know if you have any further suggestions!

[lightninglabs-deploy]

@Euler-B, remember to re-request review from reviewers when ready

[Euler-B]

@Liongrass I have completed the requested changes and the PR is ready for review. Thank you!"

[Euler-B]

/gemini review

[gemini-code-assist]

Code Review

This pull request provides a great update to the Docker-based step-by-step guide for sending payments. Focusing on simnet and removing the obsolete faucet information makes the guide much more approachable and reliable for newcomers. The updates to use the modern docker compose syntax and improve the Docker configurations with version pinning, health checks, and more secure defaults are excellent enhancements. I have one minor suggestion to improve the clarity of the documentation.

[gemini-code-assist]

For better clarity and consistency, consider changing docker to docker compose. While docker compose is part of the docker CLI, the next sentence specifically mentions the docker-compose config file. Using docker compose explicitly would make it clearer to the user which tool is being referred to, especially since the rest of the document has been updated to use the docker compose syntax.

Suggested change

	the Lightning Network Daemon (`lnd`). This folder uses `docker` to
	package `lnd` and `btcd` together to make deploying the two daemons as easy as
	typing a few commands. All configuration between `lnd` and `btcd` are handled
	automatically by their `docker-compose` config file.
	the Lightning Network Daemon (`lnd`). This folder uses `docker compose` to
	package `lnd` and `btcd` together to make deploying the two daemons as easy as
	typing a few commands. All configuration between `lnd` and `btcd` are handled
	automatically by their `docker-compose` config file.

[Euler-B]

/gemini review

[gemini-code-assist]

Code Review

This pull request provides a great update to the Docker-based step-by-step guide for sending payments. The focus on simnet, removal of obsolete information about the faucet, and updates to use modern Docker commands and practices significantly improve the guide's usability and reliability for new developers. The Dockerfile enhancements, such as version pinning, adding a health check, and improving security defaults, are also valuable contributions. I've found one minor inconsistency in the documentation that I've commented on. Overall, this is a solid improvement.