Implement server-side role management

Signed-off-by: Cole Miller <cole.miller@canonical.com>

.github/workflows/build-and-test.yml

@@ -31,7 +31,7 @@ jobs:
  env:
  CC: ${{ matrix.compiler }}
  run: |
- git clone https://github.com/canonical/raft.git --depth 1
+ git clone https://github.com/cole-miller/raft.git --branch transfer-clone --depth 1
  cd raft
  autoreconf -i
  ./configure --enable-debug --enable-sanitize

Makefile.am

@@ -36,6 +36,7 @@ libdqlite_la_SOURCES = \
  src/registry.c \
  src/request.c \
  src/response.c \
+ src/role_management.c \
  src/server.c \
  src/stmt.c \
  src/tracing.c \
@@ -86,6 +87,7 @@ unit_test_SOURCES += \
  test/unit/test_registry.c \
  test/unit/test_replication.c \
  test/unit/test_request.c \
+ test/unit/test_role_management.c \
  test/unit/test_tuple.c \
  test/unit/test_vfs.c \
  test/unit/main.c
@@ -99,6 +101,7 @@ integration_test_SOURCES = \
  test/integration/test_fsm.c \
  test/integration/test_membership.c \
  test/integration/test_node.c \
+ test/integration/test_role_management.c \
  test/integration/test_vfs.c \
  test/integration/main.c
 integration_test_CFLAGS = $(AM_CFLAGS) -Wno-conversion

include/dqlite.h

@@ -208,14 +208,45 @@ int dqlite_node_set_snapshot_params(dqlite_node *n, unsigned snapshot_threshold,
 int dqlite_node_enable_disk_mode(dqlite_node *n);
 
 /**
- * Start a dqlite node.
+ * Set the target number of voting nodes for the cluster.
  *
- * A background thread will be spawned which will run the node's main loop. If
- * this function returns successfully, the dqlite node is ready to accept new
- * connections.
+ * If automatic role management is enabled, the cluster leader will attempt to
+ * promote nodes to reach the target. If automatic role management is disabled,
+ * this has no effect.
+ *
+ * The default target is 3 voters.
+ */
+ int dqlite_node_set_target_voters(dqlite_node *n, int voters);
+
+/**
+ * Set the target number of standby nodes for the cluster.
+ *
+ * If automatic role management is enabled, the cluster leader will attempt to
+ * promote nodes to reach the target. If automatic role management is disabled,
+ * this has no effect.
+ *
+ * The default target is 0 standbys.
+ */
+ int dqlite_node_set_target_standbys(dqlite_node *n, int standbys);
+
+ /**
+ * Enable automatic role management on the server side for this node.
+ *
+ * By default, no automatic role management is performed.
+ */
+ int dqlite_node_enable_role_management(dqlite_node *n);
+
+ /**
+ * Start a dqlite node.
+ *
+ * A background thread will be spawned which will run the node's main loop. If
+ * this function returns successfully, the dqlite node is ready to accept new
+ * connections.
  */
 int dqlite_node_start(dqlite_node *n);
 
+int dqlite_node_handover(dqlite_node *n);
+
 /**
  * Stop a dqlite node.
  *

src/config.c

@@ -50,6 +50,8 @@ int config__init(struct config *c, dqlite_node_id id,
  strncpy(c->dir, dir, sizeof(c->dir)-1);
  c->dir[sizeof(c->dir)-1] = '\0';
  c->disk = false;
+ c->voters = 3;
+ c->standbys = 0;
  serial++;
  return 0;
 }

src/config.h

@@ -8,17 +8,19 @@
  */
 struct config
 {
- dqlite_node_id id; /* Unique instance ID */
- char *address; /* Instance address */
- unsigned heartbeat_timeout; /* In milliseconds */
- unsigned page_size; /* Database page size */
- unsigned checkpoint_threshold; /* In outstanding WAL frames */
- struct logger logger; /* Custom logger */
- char name[256]; /* VFS/replication registriatio name */
+ dqlite_node_id id;  /* Unique instance ID */
+ char *address;  /* Instance address */
+ unsigned heartbeat_timeout;  /* In milliseconds */
+ unsigned page_size;  /* Database page size */
+ unsigned checkpoint_threshold;  /* In outstanding WAL frames */
+ struct logger logger;  /* Custom logger */
+ char name[256];  /* VFS/replication registriatio name */
  unsigned long long failure_domain; /* User-provided failure domain */
  unsigned long long int weight; /* User-provided node weight */
- char dir[1024]; /* Data dir for on-disk database */
- bool disk; /* Disk-mode or not */
+ char dir[1024]; /* Data dir for on-disk database */
+ bool disk; /* Disk-mode or not */
+ int voters; /* Target number of voters */
+ int standbys; /* Target number of standbys */
 };
 
 /**