fips/docs/tutorials/resolve-peers-via-nostr.md

Resolve Peer Addresses via Nostr

After persistent-identity, your daemon has a stable npub and is peered with test-us01 over a hard-coded UDP address (test-us01.fips.network:2121). That static address works fine until test-us01 moves to a new IP, swaps ports, or starts publishing additional endpoints you'd want to reach. The npub is stable; the set of network endpoints behind it may not be.

This tutorial shows the smallest useful step toward Nostr- mediated discovery: keep the peer entry but drop its address, let your daemon ask public Nostr relays for the peer's current endpoint, and verify the link still works. You will not be publishing anything yourself yet — this is the consume-only case.

The whole exercise should take about ten minutes.

What you'll build

                        ┌──────────────────────────┐
                        │  Nostr relays            │
                        │   relay.damus.io         │
                        │   nos.lol                │
                        │   offchain.pub           │
                        └────────────▲─────────────┘
   "what's test-us01's                │ signed advert
    current address?"                 │ (Kind 37195)
                                      │ from test-us01
   ┌───────────────────────┐          │
   │   your fips daemon    │ ─────────┘
   │   peers:              │
   │     - test-us01 npub  │ ─── dial resolved UDP ──▶ test-us01
   │       via_nostr: true │
   └───────────────────────┘

You'll change two things in /etc/fips/fips.yaml:

• Add a node.discovery.nostr block that turns the consume- side of Nostr discovery on.
• Edit the existing test-us01 peer entry to drop its hard- coded addresses: block and add via_nostr: true.

After restart, the daemon will fetch test-us01's current advert from the relays, use the endpoint listed there, and peer normally.

How Nostr discovery resolves an address

Every FIPS daemon with node.discovery.nostr.advertise: true publishes a signed Nostr event (Kind 37195) listing the transport endpoints it is willing to accept connections on. The event is signed by the daemon's secret key, so anyone who has the corresponding npub can verify the advert really came from that node.

test-us01 runs with advertise: true. Its current advert is visible to any Nostr client.

Identity is stable; endpoints are not. A peer's npub is a long-lived identifier — it is who they are. Their UDP address, port, or transport choice is metadata that may change. Nostr discovery lets you bind your peer entry to the npub and lets the relay tell your daemon the current endpoint at dial time.

There are two halves to this — consuming adverts (looking up peers by npub) and publishing adverts (being lookup-able). This tutorial covers only the consume half.

Consume vs. publish. This tutorial enables only the consume side: your daemon queries relays to resolve peers by npub. It does not publish an advert of its own — others still cannot find you by your npub yet. The next tutorial (advertise-your-node) handles the publish side.

Step 1: Confirm your starting state

You should currently have:

• A persistent npub from persistent-identity. Confirm:

  sudo fipsctl show status | grep '"npub"'
  

• A working static peering with test-us01. Confirm:

  sudo fipsctl show peers
  

  Expect test-us01 listed with connectivity active and a transport_addr of roughly test-us01.fips.network:2121.

If either of those isn't true, finish the previous two tutorials first; the Nostr discovery layer is built on top of that working state.

Step 2: Enable the consume side of Nostr discovery

Open /etc/fips/fips.yaml and add a discovery block under node::

node:
  identity:
    persistent: true
  discovery:
    nostr:
      enabled: true
      advertise: false

Two knobs, one job each:

• enabled: true turns on the Nostr discovery runtime — the daemon connects to a default relay set (wss://relay.damus.io, wss://nos.lol, wss://offchain.pub) and is now able to query and consume adverts.
• advertise: false keeps the publish side off. Your daemon will not publish an advert of its own at this stage. The default is true, so we are setting it explicitly to disable advertising for this consume-only tutorial. The next tutorial flips it back on.

Step 3: Switch the peer entry to via_nostr

Find the peers: block you added during join-the-test-mesh and change it from this:

peers:
  - npub: "npub1qmc3cvfz0yu2hx96nq3gp55zdan2qclealn7xshgr448d3nh6lks7zel98"
    alias: "test-us01"
    addresses:
      - transport: udp
        addr: "test-us01.fips.network:2121"
    connect_policy: auto_connect

to this:

peers:
  - npub: "npub1qmc3cvfz0yu2hx96nq3gp55zdan2qclealn7xshgr448d3nh6lks7zel98"
    alias: "test-us01"
    via_nostr: true
    connect_policy: auto_connect

What changed: the addresses: list is gone, replaced by via_nostr: true. The npub stays — it is what the daemon matches against the advert publisher's pubkey.

Save the file.

Step 4: Restart the daemon

sudo systemctl restart fips
sudo systemctl status fips

The status output should show active (running) within a couple of seconds. The Nostr discovery runtime starts alongside the rest of the daemon, fetches test-us01's advert from the default relays, and uses the endpoint listed there to dial.

The resolution itself happens at debug-log level, so you will not see it in the default-level journal. The user-facing way to confirm everything worked is fipsctl show peers in the next step. (To watch the resolution in the journal, run the daemon manually with RUST_LOG=fips::nostr=debug; not necessary for this tutorial.)

Step 5: Verify the resolved endpoint

sudo fipsctl show peers

test-us01 should appear with connectivity active and a transport_addr reflecting the address that was resolved from the advert — test-us01.fips.network:2121 at time of writing. That field is the strong signal: nothing in your config gave the daemon that IP, yet there it is.

You can confirm independently that the address came from the advert. The advert is a public Nostr event — anyone can fetch it. With the nak Nostr CLI installed:

nak req -k 37195 -d "fips-overlay-v1" \
    -a 06f11c31227938ab98ba982280d2826f66a063f9efe7e342e81d6a76c677d7ed \
    --limit 1 wss://relay.damus.io

(That hex pubkey is the same identity as npub1qmc3...zel98 — Nostr filters take hex.) The content field of the returned event lists the endpoints array; one of its entries should match what fipsctl show peers is using. That is what your daemon just did, signed and verified by the Nostr layer.

Step 6: Confirm reachability still works

ping6 -c 4 test-us01.fips

Expect four replies, exactly as in join-the-test-mesh (which used the full npub form). Nothing about the data plane has changed; only the way you discovered the endpoint to dial.

What you've learned

• Adverts are signed. Every Nostr discovery advert is signed by the publisher's secret key, so the address you resolved through a public relay is trustworthy in the same sense the peer's npub is.
• via_nostr replaces a static address. A peer entry with no addresses: block and via_nostr: true directs the daemon to look the endpoint up at dial time.
• The relay set is small and public. Three default relays today; the daemon round-robins queries across them. No central FIPS infrastructure is involved.
• Static and Nostr can mix. You replaced the static address with via_nostr here, but you could have kept both — when both are present, static endpoints are tried first and Nostr-resolved endpoints are appended as a fallback. Useful when you want a fast-path direct dial but a resilient fallback.

Troubleshooting

If the link does not come up:

• No advert on the relays. If the peer's daemon is offline or has advertise: false, no advert exists for your daemon to consume. Verify with nak (Step 5) — if the query returns nothing, that is the problem and it is on the peer's side. Re-add the static addresses: entry as a fallback while you wait for the peer to come back up.
• Relay reachability. Connected to relay lines should appear for at least one of the three default relays. If none do, your network may be filtering outbound WebSocket traffic or DNS for those hostnames. Check the journal for TLS/DNS errors.
• Stale cache. The daemon caches resolved endpoints briefly. If a peer's advert changes mid-session and you hit a stale entry, restart the daemon to force a fresh query.
• Persistent identity not on. If the journal shows Using ephemeral identity (new keypair each start), the daemon falls back to ephemeral and the consume-side may not behave as expected. Re-check persistent-identity Step 2.

What's next

• Advertise your own node. advertise-your-node publishes your daemon's UDP endpoint on Nostr so other operators can add you to their peers: list with via_nostr: true and reach you the way you just reached test-us01. Includes a short final section on udp:nat, the best-effort hole-punching path for nodes without a directly reachable UDP endpoint.

• Discover peers with no prior configuration. open-discovery switches your daemon to policy: open so the ambient namespace itself populates your peer list — no static peers: entries required (the static ones can stay too; the two mechanisms run in parallel).

For the operator-style scenario reference covering all five shapes of Nostr discovery side-by-side (consume-only, publish-direct, publish-Tor, NAT traversal, open):

• ../how-to/enable-nostr-discovery.md — five scenarios with minimal YAML fragments.

For the design and security model:

• ../design/fips-nostr-discovery.md — discovery runtime architecture, advert format, threat model.

For the wire-format details:

• ../reference/nostr-events.md — Kind 37195 advert format, Kind 21059 traversal signaling, Kind 10050 inbox-relay list.