Embed etcd into hydra-node (#1992)

By compiling `etcd` into `hydra-node` we can get rid of the runtime
dependency onto `etcd` in exchange for a build-time dependency and
bigger binary size.


![image](https://github.com/user-attachments/assets/9cc82b87-3d92-4ad3-aec8-ef0895375d0f)

While I was worried that we would need a static compiled `etcd`, it
turns out the default one is already a static binary (likely because
it's a go project!):

```
λ ldd $(realpath $(which etcd))
	not a dynamic executable
```

That means, all our `hydra-node` builds contain a statically linked
`etcd` binary now.

## File sizes

Dynamic linked `hydra-node`:
```
λ ll $(nix build .#hydra-node --print-out-paths)/bin/hydra-node
warning: Git tree '/home/ch1bo/code/iog/hydra' is dirty
warning: Git tree '/home/ch1bo/code/iog/hydra' is dirty
.r-xr-xr-x root root 90 MB Thu Jan  1 01:00:01 1970  /nix/store/mca588qi4glryha0d1kkg4s0lmbw6xqk-hydra-node/bin/hydra-node
```

Static linked `hydra-node`:
```
λ ll $(nix build .#hydra-node-static --print-out-paths)/bin/hydra-node
warning: Git tree '/home/ch1bo/code/iog/hydra' is dirty
warning: Git tree '/home/ch1bo/code/iog/hydra' is dirty
.r-xr-xr-x root root 94 MB Thu Jan  1 01:00:01 1970  /nix/store/q3dr4fa7w3iy2rqrwp0xgr8bk364s6ka-hydra-node-x86_64-unknown-linux-musl/bin/hydra-node
```

Compressed (and darwin):

![image](https://github.com/user-attachments/assets/329680e3-f830-4310-8710-4a2ad22a8d56)

## Try it please
It's unclear whether this works for all target platforms. To try it,
download the binary of your platform from this CI action
https://github.com/cardano-scaling/hydra/actions/workflows/binaries.yaml?query=branch%3Aembed-etcd
and run

```
echo "{}" > utxo.json
./bin/hydra-node --offline-head-seed 01 --initial-utxo utxo.json --ledger-protocol-parameters hydra-cluster/config/protocol-parameters.json --persistence-dir ./tmp-etcd --node-id foo --hydra-signing-key demo/alice.sk
```

from within a hydra working copy.

---

<!-- Consider each and tick it off one way or the other -->
* [x] CHANGELOG updated
* [x] Documentation updated
* [x] Haddocks updated
* [x] No new TODOs introduced

Author: noonio

.github/workflows/binaries.yaml

@@ -6,6 +6,7 @@ on:
     branches:
     - master
     - release
+    - embed-etcd
     tags:
     - "*.*.*"
 

CHANGELOG.md

@@ -14,7 +14,10 @@ changes.
 
 - Fix tutorial usage of `cardano-cli` and include download of `etcd`.
 
-* **BREAKING** Update scripts to plutus 1.45.0.0.
+- Remove runtime dependency to `etcd` by embedding and shipping it with `hydra-node`.
+  - New option `--use-system-etcd` to prefer the system etcd instead of the embedded one.
+
+- **BREAKING** Update scripts to plutus 1.45.0.0.
 
 ## [0.21.0] - 2025-04-28
 

docs/adr/2025-02-12_032-network-properties-etcd.md

@@ -57,6 +57,7 @@ Accepted
 
 - Using `etcd` as-is adds a run-time dependency onto that binary.
   - Docker image users should not see any different UX
+  - We can ship the binary through `hydra-node`.
 
 - Introspectability network as the `etcd` cluster is queriable could improve debugging experience
 

hydra-cluster/src/HydraNode.hs

@@ -23,7 +23,7 @@ import Hydra.API.HTTPServer (DraftCommitTxRequest (..), DraftCommitTxResponse (.
 import Hydra.Cluster.Util (readConfigFile)
 import Hydra.HeadLogic.State (SeenSnapshot)
 import Hydra.Logging (Tracer, Verbosity (..), traceWith)
-import Hydra.Network (Host (Host), NodeId (NodeId))
+import Hydra.Network (Host (Host), NodeId (NodeId), WhichEtcd (EmbeddedEtcd))
 import Hydra.Network qualified as Network
 import Hydra.Options (ChainConfig (..), DirectChainConfig (..), LedgerConfig (..), RunOptions (..), defaultDirectChainConfig, toArgs)
 import Hydra.Tx (ConfirmedSnapshot)
@@ -399,6 +399,7 @@ prepareHydraNode chainConfig workDir hydraNodeId hydraSKey hydraVKeys allNodeIds
       , hydraVerificationKeys
       , persistenceDir = stateDir
       , chainConfig
+      , whichEtcd = EmbeddedEtcd
       , ledgerConfig =
           CardanoLedgerConfig
             { cardanoLedgerProtocolParametersFile
@@ -518,6 +519,7 @@ withHydraNode tracer chainConfig workDir hydraNodeId hydraSKey hydraVKeys allNod
                 , hydraVerificationKeys
                 , persistenceDir = stateDir
                 , chainConfig
+                , whichEtcd = EmbeddedEtcd
                 , ledgerConfig =
                     CardanoLedgerConfig
                       { cardanoLedgerProtocolParametersFile