Use RPC for friendbot when available

[leighmcculloch]

What

Use the RPC backend support of friendbot instead of Horizon. Update startup script to wait for either RPC or Horizon based on configuration. Remove hardcoded horizon_url from config and dynamically inject the appropriate backend URL. Allow friendbot to start when only RPC is enabled without requiring Horizon.

Why

Friendbot previously required Horizon to fund accounts. With RPC support, friendbot can operate in RPC-only deployments without needing Horizon running. RPC is the preferred integration point, because in the future Friendbot will support funding contracts, and so even if both RPC and Horizon are available it will default to RPC to be able to support contract functionality.

Merging

Dependent on:

• Add interface between app logic and horizon client for port to rpc friendbot#17
• Add RPC integration friendbot#20

Cannot be merged until all images are updated to use a version of friendbot that contains the two dependent changes above.

Testing

This change includes a new image, friendbot-with-rpc, temporarily just while in pull request that can be used for testing the dependent changes above.

Close stellar/friendbot#5
Close #791

[Copilot]

Pull request overview

This pull request enables friendbot to use RPC as its backend instead of requiring Horizon, supporting RPC-only deployments. The changes allow friendbot to dynamically configure either RPC or Horizon backends, with RPC being the preferred option when both are available to support future contract funding functionality.

• Removed hardcoded horizon_url from friendbot config and made backend URL injection dynamic based on which service is enabled
• Updated startup scripts to conditionally wait for either RPC or Horizon based on friendbot's configuration
• Removed the forced enabling of Horizon when RPC is enabled for local networks

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 2 comments.

File	Description
start	Removed forced ENABLE_HORIZON when ENABLE_RPC is true; added dynamic backend URL injection in init_friendbot(); updated upgrade_local() to start friendbot when either RPC or Horizon is enabled
common/friendbot/etc/friendbot.cfg	Removed hardcoded horizon_url to allow dynamic backend configuration
common/friendbot/bin/start	Added conditional waiting logic for RPC and Horizon backends based on configuration file contents
images.json	Added temporary "friendbot-with-rpc" image for testing the dependent friendbot changes with specific commit reference

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[sreuland]

looks good, left one comment on friendbot startup config.

[leighmcculloch]

TODO:

• Figure out how to prevent the intermittent race condition with friendbot starting too early because RPC is available earlier than Horizon used to be:
  Failure: https://github.com/stellar/quickstart/actions/runs/19964021280/job/57251384889?pr=840
  Failure: https://github.com/stellar/quickstart/actions/runs/19964021280/job/57252619314?pr=840
  Success: https://github.com/stellar/quickstart/actions/runs/19964021280/job/57256102817?pr=840

[leighmcculloch]

The intermittent race condition failure is difficult to debug because the container log collection is broken.

Opened issue to track fixing that:

• "Prepare Test Logs" step fails when container has stopped early #847

And pull request with fix:

• Fix log collection when container stops early #848

[leighmcculloch]

This is an example of intermittent failure now that the logging has been fixed:

• https://github.com/stellar/quickstart/actions/runs/20011266152/job/57383019778?pr=840

[leighmcculloch]

These are Friendbot logs. It looks like it's failing trying to create the minion accounts.

Waiting for rpc to be available...
starting friendbot...
time="2025-12-07T23:31:03.005Z" level=info msg="Tracing disabled - using no-op tracer" pid=759
time="2025-12-07T23:31:03.005Z" level=info msg="Tracer initialized" pid=759
2025/12/07 23:31:03 Found all valid params, now creating 10 minions
2025/12/07 23:31:03 Creating 10 new minion accounts
time="2025-12-07T23:31:03.146Z" level=error msg="creating minion accounts: submitting create accounts tx: transaction rejected" pid=759