lantern

Lantern — the in-memory Key-Vertex-Store

Lantern is a cache that understands relationships. It is a Key-Vertex-Store: you use it like the key-value cache you already run — put, get, TTL — but every value is a vertex, and weighted, decaying edges connect them. So alongside "get me this value", your request-path code can ask, in a single millisecond-scale RPC:

• "What's near this key right now?" — illuminate walks the live graph and returns a subgraph already shaped for your use case (k-NN, spanning tree, shortest paths, PageRank, community).
• "How strongly are these two related at this moment?" — edge weights are live sums of TTL'd contributions, so relationship strength decays on its own as events age out.
• "Which keys match these words?" — BM25 full-text search over vertex content, with fuzzy/phrase/prefix matching, built into the same store.

No nightly graph pipeline, no heavyweight graph database on the hot path, no fetching a wall of edges to post-process in your service. The graph lives where cache data lives: in memory, with TTLs, in front of your system of record.

> put vertex user:42 "alice"
> put vertex item:7  "lamp"
> add edge user:42 item:7 1.0 1800     # each event appends a decaying contribution
> illuminate user:42 2 10              # 2 hops out, top-10 per hop — one RPC
{ "vertices": { ... }, "edges": { ... } }

Those three writes just built a live graph:

graph LR
    u(("user:42<br/>alice")) -- "1.0 · ttl 30m" --> i(("item:7<br/>lamp"))

Everything speaks the Connect protocol — with gRPC and gRPC-Web wire compatibility on the same h2c socket — so Go services, browsers, CLIs, and anything with a protobuf toolchain hit the identical API on one port.

Status: pre-1.0 — expect breaking changes. Until v1.0.0, Lantern makes no backward-compatibility guarantees: the proto/wire schema, SDK APIs, CLI grammar, LANTERN_* env vars, and metric names can change between releases. Pin a version if you need stability.

Why a graph in your cache?

Most graph stores are built for offline analytics over yesterday's snapshot. Most caches flatten relationships away entirely. Lantern sits in the gap: online, behavioral graph data with cache semantics.

Never used a graph? It's just entries + connections

A key-value cache stores isolated entries. Lantern turns those entries into a graph in the mathematical sense — the weighted directed graph of graph theory, G = (V, E, w): vertices, directed edges between them, a real-valued weight on each edge, and (Lantern's cache-native twist) a TTL on all of it. Not the property graph of graph databases, with typed, attribute-laden edges — the plain mathematical object. Same data, one new dimension:

flowchart TB
    subgraph before["A classic KVS — every entry is an island"]
        a1["user:42 = alice"]
        a2["user:99 = bob"]
        a3["item:7 = lamp"]
        a4["item:9 = desk"]
    end
    subgraph after["A Key-Vertex-Store — the same entries, connected"]
        direction LR
        u42(("user:42<br/>alice")) -- "1.5" --> i7(("item:7<br/>lamp"))
        u42 -- "0.3" --> i9(("item:9<br/>desk"))
        u99(("user:99<br/>bob")) -- "2.0" --> i7
    end
    before -->|"add edge …"| after

That's the entire vocabulary you need:

• Vertex — one cache entry: a key and its value (user:42 = alice), with a TTL.
• Edge — an ordered pair of keys with a weight and a TTL: one element of E, nothing more — no type, label, or property bag. If you need relationship kinds ("clicked" vs "bought"), encode them in your key design or weight conventions.
• Weight — how strong that link is right now. In Lantern it's the live sum of decaying contributions, so recent events count more than old ones.
• TTL — everything above expires on its own; nothing needs a cleanup job.

Staying with the mathematical object is deliberate — it is what keeps the rest of Lantern simple and fast:

• The classic algorithms apply directly. Spanning trees, shortest paths, PageRank, community detection — graph theory defines them on exactly this object, a weighted directed graph. illuminate runs them natively over every edge, with no "which relationship types does this walk follow?" configuration and no schema the server has to know about; a property graph has to be flattened down to weights before any of that theory applies.
• Every event can pile onto the same edge. The additive, decaying weight model works because merging contributions is just addition — there are no per-type aggregation rules to define.
• Nothing to design up front, nothing to migrate. A new kind of event starts flowing into the graph the moment you write it — cache semantics extend to the data model itself.
• Edges stay tiny. A contribution is a weight and an expiration, which is why a large working set fits in one process's memory in the first place.

The payoff: questions like "what has this user interacted with lately, and how strongly?" stop being JOINs over event logs in your warehouse and become a one-RPC lookup against the cache.

TTLs on everything — including edges

Every vertex and every edge can carry its own expiration. A background janitor compacts expired entries and prunes edges whose endpoints vanished. The working set stays warm and small without manual deletes: the graph forgets old information the same way real-world relationships fade.

Edge weights that accumulate — and decay

Edges are not single scalars. Each add edge appends another contribution with its own TTL; the reported weight is the live sum of contributions that have not yet expired:

t=0   add edge a b 1.0 ttl=3s    →  weight(a,b) = 1
t=1   add edge a b 1.0 ttl=3s    →  weight(a,b) = 2   (two contributions live)
t=3   first contribution expires →  weight(a,b) = 1
t=4   second expires             →  weight(a,b) = 0   (edge gc'd)

xychart-beta
    title "weight(a,b) over time — two 1.0 contributions, each ttl=3s"
    x-axis "seconds" [0, 1, 2, 3, 4]
    y-axis "live weight" 0 --> 2.5
    line [1, 2, 2, 1, 0]

This is the model behavioral signals actually want: every click, view, or co-occurrence is one append, and "how strong is this relationship right now" falls out of the math — no batch job. Need classic idempotent replace instead? That's put edge.

Vertices also auto-materialize on edge writes (inheriting the edge's TTL), so ingesting an event stream is just a stream of edge writes.

Graph queries as single RPCs

One Illuminate call walks the live graph from a seed and returns exactly the shape you asked for. Three orthogonal axes select it:

Seeing is believing. Say the store holds this graph (labels are weights):

graph LR
    a((a)) -- 1 --> b((b))
    a -- 1 --> c((c))
    b -- 2 --> d((d))
    b -- 3 --> e((e))
    c -- 1 --> e
    c -- 4 --> f((f))

illuminate a 2 2 algorithm=spt objective=max treats heavy edges as cheap (cost = 1/weight), so one RPC hands back the strongest-relationship tree — no client-side post-processing:

graph LR
    a((a)) -- 1 --> b((b))
    a -- 1 --> c((c))
    b -- 3 --> e((e))
    c -- 4 --> f((f))

Flip to objective=min and weights become costs: the same RPC now returns the cheapest-path tree, reaching e via c (cost 1+1) instead of via b (cost 1+3):

graph LR
    a((a)) -- 1 --> b((b))
    a -- 1 --> c((c))
    b -- 2 --> d((d))
    c -- 1 --> e((e))

A few more combinations and what they buy you:

illuminate user:42 2 10                              # raw 2-hop neighbourhood
illuminate user:42 3 8 algorithm=spt objective=max   # most-relevant path tree
illuminate user:42 3 8 algorithm=mst objective=min   # clustering / dedup backbone
illuminate user:42 2 10 algorithm=ppr                # PageRank-ranked neighbourhood
illuminate user:42 2 10 algorithm=community          # the seed's natural community
illuminate user:42 2 10 weighting=tfidf              # suppress hub items

PPR takes two locality knobs (restart_prob, epsilon — higher restart keeps the walk closer to the seed; smaller epsilon pushes further for more recall). A prefix= filter restricts the walk to a key namespace during traversal, yielding the prefix-induced subgraph — note that with mst/spt a matching vertex reachable only through a non-matching bridge is excluded, because the bridge is not traversable.

Full-text search over the same store

SearchVertices runs relevance-ranked (BM25) full-text search over vertex content — key plus value — as the content-addressed counterpart to prefix scans. Ranked hits make natural seeds for a follow-up illuminate:

lantern-cli search "rolling update"              # OR-union of the query words
lantern-cli search "rolling update" --mode all   # require every word (AND)
lantern-cli search "rolling update" --phrase     # adjacent, in order
lantern-cli search serach --fuzziness 1          # typos still hit
lantern-cli search lan --prefix-terms            # "lan" finds "lantern"
lantern-cli search espresso --prefix user.       # scope to a key namespace

The index is maintained server-side and is on by default (LANTERN_SEARCH_ENABLED).

Try it in 60 seconds

Start a server (Docker, Homebrew, or source):

docker run --rm -p 6380:6380 ghcr.io/anaregdesign/lantern:latest

# or on macOS:
brew tap anaregdesign/tap
brew install --cask lantern        # server (binary: lantern)
brew install --cask lantern-cli    # client (binary: lantern-cli)

# or from source:
go run ./server/cmd                # listens on :6380

Then poke at it with the CLI — lantern-cli repl for an interactive prompt, or the same grammar as verb-first one-liners:

$ lantern-cli repl
> put vertex alice Alice
OK (1.2ms)
> put vertex bob Bob 3600               # third arg = TTL seconds
OK (0.9ms)
> add edge alice bob 1.5 3600           # additive: appends a contribution
OK (1.1ms)
> add edge alice bob 0.5 3600           # second contribution
OK (0.8ms)
> get edge alice bob                    # live sum of unexpired contributions
2.000000
OK (0.6ms)
> illuminate alice 2 5
{
        "vertices": { ... },
        "edges":    { ... }
}
OK (2.3ms)

Prefer a UI? One docker compose up brings up a 3-replica HA cluster, the browser Admin console, and Prometheus — see Deploying.

Use it from your language

Go

The Go SDK is its own module — external projects pull only Connect-Go and protobuf, nothing from the server:

go get github.com/anaregdesign/lantern/sdks/go

import "github.com/anaregdesign/lantern/sdks/go"

cli, err := client.NewLantern("localhost:6380")
if err != nil { log.Fatal(err) }
defer cli.Close()

ctx := context.Background()

// Vertices accept string, int, float, bool, time.Time, time.Duration, []byte, nil.
_ = cli.PutVertex(ctx, "user:42", "alice", 1*time.Hour)
_ = cli.PutVertex(ctx, "item:7",  "lamp",  1*time.Hour)

// Each AddEdge appends a contribution with its own TTL and returns the live sum.
_, _ = cli.AddEdge(ctx, "user:42", "item:7", 1.0, 30*time.Minute)

// Walk: 2 hops, top-3 per hop, TF-IDF weighted.
g, _ := cli.Illuminate(ctx, "user:42",
    client.WithBFS(client.BFSOpts{Step: 2, FanOut: 3}),
    client.WithWeighting(client.WeightingTFIDF))

// Full-text search: BM25-ranked hits over vertex content.
hits, _ := cli.SearchVertices(ctx, "desk lamp", client.WithMatchMode(client.MatchAll))

// Prefix scan: enumerate a namespace, auto-paginated.
for batch, err := range cli.ScanVerticesAll(ctx, "user:", 100) {
    if err != nil { log.Fatal(err) }
    for _, v := range batch { fmt.Println(client.StringValue(v)) }
}

Operational tiers compose in: client.WithAuthToken for bearer-token servers, client.WithRetry for opt-in full-jitter retries (applied only to RPCs that are idempotent under your configuration), and client.NewLanternFailover for sticky-cursor rotation across HA replicas. Full worked example: sdks/go/example/main.go.

TypeScript / Node

Ships to npm as lantern-sdk (ESM + CJS, bundled types, Node 20+):

npm install lantern-sdk

import { connect } from "lantern-sdk";

const client = connect("http://localhost:6380");
try {
  await client.putVertex({ key: "user:42", value: "alice", ttlSeconds: 3600 });
  await client.addEdge({ tail: "user:42", head: "item:7", weight: 1.0, ttlSeconds: 1800 });

  const graph = await client.illuminate("user:42", { step: 2, k: 16 });
  const hits  = await client.searchVertices("desk lamp", { limit: 10 });

  for await (const page of client.scanVerticesAll("user:", 500)) {
    for (const v of page) console.log(v.key);
  }
} finally {
  client.close();
}

JS values map to typed proto fields (string, number, bigint, boolean, Date, Uint8Array, null, plus explicit numeric wrappers); batch writes auto-chunk. The browser build (lantern-sdk/web) is what powers the admin SPA. Full API: sdks/node/README.md.

Anything else

Generate bindings from proto/graph/v1/graph.proto with buf, protoc, or any Connect codegen plugin. The server multiplexes Connect (JSON or proto), gRPC, and gRPC-Web over the same :6380 h2c socket — no sidecar, no gateway.

When to use it (and when not)

Good fit

• Real-time recommenders — user → item interactions as decaying edges; illuminate(user, step=2, k=10, weighting=tfidf) returns a candidate set that already discounts popular items.
• Session-aware personalization — a short-TTL session graph layered on a long-TTL preference graph in the same store.
• Fraud / abuse co-occurrence — accounts, devices, IPs as vertices; suspicious co-occurrences as additive edges that self-clean as they decay.
• Trend detection — query → result edges tick up on each interaction and fall off when the trend dies.
• Online graph features for ML — neighborhood aggregations served at request time instead of from a batch feature store.
• Short-lived shared context for agents / sessions — entity-relation state scoped to a session TTL, queried with illuminate.

Not a good fit

• Durability out of the box. Lantern is in-memory: a restart loses the graph (a periodic snapshot backup with restore-on-boot is built in, but there is no WAL). Replay your event stream on boot, or put a queue in front.
• Whole-graph analytics — global PageRank, community detection across billions of edges. (Seed-local PPR and community via illuminate are supported online queries.)
• Working sets beyond one process's RAM. Built-in leaderless replication gives you HA — every replica holds the full graph — but there is no sharding.
• Strong-consistency multi-writer. The store is a leaderless full-replica cache with last-writer-wins per key under an HLC clock, not a linearizable database.

Architecture at a glance

flowchart LR
    subgraph Clients
        Admin["lantern-admin (admin/)<br/>browser console"]
        GoSDK["sdks/go"]
        NodeSDK["sdks/node"]
        CLI["lantern-cli"]
        MCP["lantern-mcp (mcp/)"]
        Other3P["any Connect / gRPC /<br/>gRPC-Web client"]
    end

    Admin   -->|Connect-Web| SVC
    GoSDK   -->|Connect / gRPC| SVC
    NodeSDK -->|Connect / gRPC| SVC
    CLI     -->|Connect / gRPC| SVC
    MCP     -->|via sdks/go| SVC
    Other3P -->|":6380 (one h2c socket)"| SVC

    subgraph Server["lantern-server — one of N full replicas"]
        direction TB
        SVC["LanternService"]
        VC["vertex cache (TTL)"]
        EC["edge cache (additive + TTL)"]
        IX["search index (BM25)"]
        W["GC loop"]
        Repl["replication pump<br/>(HLC + mutation log)"]
        SVC --> VC
        SVC --> EC
        SVC --> IX
        W -.compacts.-> VC
        W -.compacts.-> EC
        SVC <--> Repl
    end

    Peers[("peer replicas<br/>(HA mode)")]
    Repl <-->|Subscribe / Snapshot| Peers

• One wire surface. The :6380 listener accepts Connect, gRPC, and gRPC-Web on the same h2c socket; every client in this repo — the Admin SPA, both SDKs, the CLI, the MCP server — shares the exact contract from proto/graph/v1/.
• HA is optional and leaderless. Every replica holds the full graph; writes commit locally and fan out asynchronously via Subscribe / Snapshot streams tagged with HLC timestamps. No leader, no quorum, no external storage. External CDC consumers attach Subscribe to any one replica and observe every cluster mutation. RFC: docs/replication.md; operator playbook: docs/ha-runbook.md.
• lantern-admin (admin/) — a browser-only React Router / Sigma.js console that talks Connect-Web straight to the server: graph visualization, data browsing, search, and a web CLI.
• lantern-mcp (mcp/) — optional Model Context Protocol server that exposes a Lantern instance as shared working context for agent fleets (presence, advisory claims, activity heat, a blackboard — all built on decaying state, where expiry is exactly the semantics you want). See mcp/README.md.

The RPC surface

Defined in proto/graph/v1/graph.proto, served by server/service/service.go. Every read, write, and delete has singular and plural forms; the plural is the canonical implementation, the singular a thin one-element facade — pick whichever reads better at the call site.

SDK batch writes auto-chunk; a validation interceptor rejects oversize keys and batches (LANTERN_MAX_KEY_LEN, LANTERN_MAX_BATCH_SIZE) and NaN/Inf weights before they touch the cache.

The CLI

One grammar, three surfaces: the interactive REPL (lantern-cli repl), verb-first shell one-liners, and the admin web /cli — they never diverge.

get    vertex   <key>
put    vertex   <key> <value> [ttl_seconds] [type=auto|string|int|float|bool|datetime|duration|json]
delete vertex   <key> [<key> …]
get    edge     <tail> <head>
add    edge     <tail> <head> <weight> [ttl_seconds]
put    edge     <tail> <head> <weight> [ttl_seconds]
delete edge     <tail> <head> [<tail> <head> …]
scan   vertices <prefix> [limit] [all=true]
scan   edges    <tail-prefix> [limit] [head=<prefix>] [all=true]
count  vertices <prefix>
delete-prefix vertices <prefix> [limit=<int>] [confirm=yes|dry_run=true]
keys   <prefix> [limit]
illuminate <seed> <step> <k> [algorithm=none|mst|spt|ppr|community] [objective=min|max] \
           [weighting=raw|tfidf|bm25] [prefix=<string>] \
           [restart_prob=<float>] [epsilon=<float>]
help
exit

# One-liners: same grammar, prefixed with the binary.
lantern-cli put vertex alice '{"name":"Alice"}' type=json
lantern-cli delete vertex alice bob carol
lantern-cli scan vertices users/ all=true > snap.json
lantern-cli delete-prefix vertices tmp/ dry_run=true

# Outside the grammar: search, streamed bulk load, and whole-graph backup.
lantern-cli search "desk lamp" --mode all --limit 20
cat edges.ndjson | lantern-cli bulk edges add -
lantern-cli dump graph.pb && lantern-cli restore graph.pb

# TLS / auth (global flags precede the verb).
lantern-cli --tls --tls-ca ./ca.pem -H lantern.example.com -p 443 get vertex alice
lantern-cli --token "$LANTERN_TOKEN" get vertex alice

Every subcommand has long-form help (lantern-cli <cmd> --help); reads emit JSON on stdout, writes print OK. Exit codes: 0 success, 1 local/parse error, 2 RPC error. Values quote C-style with "…" (escapes) or verbatim with '…'.

Pre-built binaries for Linux, macOS, and Windows (amd64 + arm64) are attached to every release; macOS users can brew install --cask lantern-cli.

Deploying

Docker Compose — cluster + Admin UI in one command

The fastest way to a running HA cluster with a browser console in front of it. One up starts three replicas, the Admin SPA, lantern-mcp, and Prometheus — no local build:

cd deploy/compose
docker compose up -d --pull always

Then open http://localhost:8080 — the Admin loads ready to illuminate, browse, search, and run ops against the live cluster. The replicas pin host ports 6380–6382 (the Admin's Gateway button picks which one to hit); Prometheus scrapes them all on :9091. Details and load balancing options: deploy/compose/README.md.

Kubernetes (HA)

The bundled Helm chart deploys a StatefulSet with DNS-based peer discovery, anti-entropy reconciliation, and a PodDisruptionBudget:

helm install lantern deploy/helm/lantern

Values reference: deploy/helm/lantern/README.md. Operational guidance (signals, partitions, upgrades, recovery): docs/ha-runbook.md.

Single instance

Run one instance with every LANTERN_PEER_* env unset and Lantern is a plain fast in-memory KVS: the peer pump is a no-op and Subscribe still works as a CDC stream. Pair it with the built-in snapshot backup (docs/backup.md) so a restart re-seeds the graph.

Container images

Published to GHCR on every release tag, multi-arch, cosign-signed: ghcr.io/anaregdesign/lantern (server), ghcr.io/anaregdesign/lantern-admin, and ghcr.io/anaregdesign/lantern-mcp.

Configuration

Everything is LANTERN_* env vars. The exhaustive, generated reference is docs/env.md — the ones you'll reach for first:

One default worth knowing: a write that omits TTL is stored permanently — decay is opt-in per write.

Observability

Production-grade out of the box — details in the source links:

• Prometheus metrics on LANTERN_METRICS_ADDR /metrics: standard grpc_server_* RPC metrics (canonical names retained so existing dashboards keep working) plus domain gauges/counters — lantern_vertices, lantern_edges, lantern_ttl_expirations_total, lantern_gc_duration_seconds, lantern_build_info.
• Structured logging via log/slog (JSON by default) with per-RPC start/finish events.
• Health checks: grpc.health.v1.Health on :6380 plus HTTP /healthz and /readyz on the metrics listener — Kubernetes probes and grpc_health_probe both work. LANTERN_DRAIN_DELAY_SECONDS gives zero-drop rolling updates.
• OpenTelemetry tracing: set OTEL_EXPORTER_OTLP_ENDPOINT and every request gets a span; without it the tracer stays noop with zero overhead.
• gRPC reflection on by default (handy for grpcurl); disable with LANTERN_REFLECTION=false.
• HTTP/2 keepalive tuning and a panic-recovery interceptor that turns panics into Internal responses with a logged stack trace.

Repository layout

A monorepo of six Go modules stitched by go.work plus two Bun-managed TypeScript packages; dependency direction is a strict DAG:

Limitations (the honest section)

• In-memory first. Snapshot backup + restore-on-boot is built in, but there is no WAL — writes between snapshots are lost on crash. Deployments needing stronger durability replay events from a durable log on boot.
• HA, not sharding. Leaderless full-replica replication is built in; the working set must still fit in one process's RAM.
• Auth is requirepass-tier. Static bearer tokens and TLS/mTLS — no users, ACLs, or per-namespace authorization. Front it with a mesh or sidecar if you need identity-based access control.
• One global sync.RWMutex on the graph cache (plus per-edge mutexes on weight aggregation). Read-heavy workloads scale well; write-very-hot keys serialize.

Contributing

Issues and PRs welcome. Start with CONTRIBUTING.md for the process contract and AGENTS.md for the full development guide (module rules, codegen, quality gate). The short version:

go build -v ./...        # build
go test ./...            # test (repeat in each submodule)
go generate ./...        # regenerate wire + protobuf stubs — zero install

License

MIT.