diff --git a/cloud/bmaas/bmdb/sessions.go b/cloud/bmaas/bmdb/sessions.go
new file mode 100644
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--- /dev/null
+++ b/cloud/bmaas/bmdb/sessions.go
@@ -0,0 +1,265 @@
+package bmdb
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"fmt"
+	"time"
+
+	"github.com/cockroachdb/cockroach-go/v2/crdb"
+	"github.com/google/uuid"
+	"github.com/lib/pq"
+	"k8s.io/klog/v2"
+
+	"source.monogon.dev/cloud/bmaas/bmdb/model"
+	"source.monogon.dev/cloud/lib/component"
+)
+
+// BMDB is the Bare Metal Database, a common schema to store information about
+// bare metal machines in CockroachDB. This struct is supposed to be
+// embedded/contained by different components that interact with the BMDB, and
+// provides a common interface to BMDB operations to these components.
+//
+// The BMDB provides two mechanisms facilitating a 'reactive work system' being
+// implemented on the bare metal machine data:
+//
+//   - Sessions, which are maintained by heartbeats by components and signal the
+//     liveness of said components to other components operating on the BMDB. These
+//     effectively extend CockroachDB's transactions to be visible as row data. Any
+//     session that is not actively being updated by a component can be expired by a
+//     component responsible for lease garbage collection.
+//   - Work locking, which bases on Sessions and allows long-standing
+//     multi-transaction work to be performed on given machines, preventing
+//     conflicting work from being performed by other components. As both Work
+//     locking and Sessions are plain row data, other components can use SQL queries
+//     to exclude machines to act on by constraining SELECT queries to not return
+//     machines with some active work being performed on them.
+type BMDB struct {
+	Config
+}
+
+// Config is the configuration of the BMDB connector.
+type Config struct {
+	Database component.CockroachConfig
+
+	// ComponentName is a human-readable name of the component connecting to the
+	// BMDB, and is stored in any Sessions managed by this component's connector.
+	ComponentName string
+	// RuntimeInfo is a human-readable 'runtime information' (eg. software version,
+	// host machine/job information, IP address, etc.) stored alongside the
+	// ComponentName in active Sessions.
+	RuntimeInfo string
+}
+
+// Open creates a new Connection to the BMDB for the calling component. Multiple
+// connections can be opened (although there is no advantage to doing so, as
+// Connections manage an underlying CockroachDB connection pool, which performs
+// required reconnects and connection pooling automatically).
+func (b *BMDB) Open(migrate bool) (*Connection, error) {
+	if migrate {
+		if b.Config.Database.Migrations == nil {
+			klog.Infof("Using default migrations source.")
+			m, err := model.MigrationsSource()
+			if err != nil {
+				klog.Exitf("failed to prepare migrations source: %w", err)
+			}
+			b.Config.Database.Migrations = m
+		}
+		if err := b.Database.MigrateUp(); err != nil {
+			return nil, fmt.Errorf("migration failed: %w", err)
+		}
+	}
+	db, err := b.Database.Connect()
+	if err != nil {
+		return nil, err
+	}
+	return &Connection{
+		bmdb: b,
+		db:   db,
+	}, nil
+}
+
+// Connection to the BMDB. Internally, this contains a sql.DB connection pool,
+// so components can (and likely should) reuse Connections as much as possible
+// internally.
+type Connection struct {
+	bmdb *BMDB
+	db   *sql.DB
+}
+
+// StartSession creates a new BMDB session which will be maintained in a
+// background goroutine as long as the given context is valid. Each Session is
+// represented by an entry in a sessions table within the BMDB, and subsequent
+// Transact calls emit SQL transactions which depend on that entry still being
+// present and up to date. A garbage collection system (to be implemented) will
+// remove expired sessions from the BMDB, but this mechanism is not necessary
+// for the session expiry mechanism to work.
+//
+// When the session becomes invalid (for example due to network partition),
+// subsequent attempts to call Transact will fail with ErrSessionExpired. This
+// means that the caller within the component is responsible for recreating a
+// new Session if a previously used one expires.
+func (c *Connection) StartSession(ctx context.Context) (*Session, error) {
+	intervalSeconds := 5
+
+	res, err := model.New(c.db).NewSession(ctx, model.NewSessionParams{
+		SessionComponentName:   c.bmdb.ComponentName,
+		SessionRuntimeInfo:     c.bmdb.RuntimeInfo,
+		SessionIntervalSeconds: int64(intervalSeconds),
+	})
+	if err != nil {
+		return nil, fmt.Errorf("creating session failed: %w", err)
+	}
+
+	klog.Infof("Started session %s", res.SessionID)
+
+	ctx2, ctxC := context.WithCancel(ctx)
+
+	s := &Session{
+		connection: c,
+		interval:   time.Duration(intervalSeconds) * time.Second,
+
+		UUID: res.SessionID,
+
+		ctx:  ctx2,
+		ctxC: ctxC,
+	}
+	go s.maintainHeartbeat(ctx2)
+	return s, nil
+}
+
+// Session is a session (identified by UUID) that has been started in the BMDB.
+// Its liveness is maintained by a background goroutine, and as long as that
+// session is alive, it can perform transactions and work on the BMDB.
+type Session struct {
+	connection *Connection
+	interval   time.Duration
+
+	UUID uuid.UUID
+
+	ctx  context.Context
+	ctxC context.CancelFunc
+}
+
+var (
+	// ErrSessionExpired is returned when attempting to Transact or Work on a
+	// Session that has expired or been canceled. Once a Session starts returning
+	// these errors, it must be re-created by another StartSession call, as no other
+	// calls will succeed.
+	ErrSessionExpired = errors.New("session expired")
+	// ErrWorkConflict is returned when attempting to Work on a Session with a
+	// process name that's already performing some work, concurrently, on the
+	// requested machine.
+	ErrWorkConflict = errors.New("conflicting work on machine")
+)
+
+// maintainHeartbeat will attempt to repeatedly poke the session at a frequency
+// twice of that of the minimum frequency mandated by the configured 5-second
+// interval. It will exit if it detects that the session cannot be maintained
+// anymore, canceling the session's internal context and causing future
+// Transact/Work calls to fail.
+func (s *Session) maintainHeartbeat(ctx context.Context) {
+	// Internal deadline, used to check whether we haven't dropped the ball on
+	// performing the updates due to a lot of transient errors.
+	deadline := time.Now().Add(s.interval)
+	for {
+		if ctx.Err() != nil {
+			klog.Infof("Session %s: context over, exiting: %v", s.UUID, ctx.Err())
+			return
+		}
+
+		err := s.Transact(ctx, func(q *model.Queries) error {
+			sessions, err := q.SessionCheck(ctx, s.UUID)
+			if err != nil {
+				return fmt.Errorf("when retrieving session: %w", err)
+			}
+			if len(sessions) < 1 {
+				return ErrSessionExpired
+			}
+			err = q.SessionPoke(ctx, s.UUID)
+			if err != nil {
+				return fmt.Errorf("when poking session: %w", err)
+			}
+			return nil
+		})
+		if err != nil {
+			klog.Errorf("Session %s: update failed: %v", s.UUID, err)
+			if errors.Is(err, ErrSessionExpired) || deadline.After(time.Now()) {
+				// No way to recover.
+				klog.Errorf("Session %s: exiting", s.UUID)
+				s.ctxC()
+				return
+			}
+			// Just retry in a bit. One second seems about right for a 5 second interval.
+			//
+			// TODO(q3k): calculate this based on the configured interval.
+			time.Sleep(time.Second)
+		}
+		// Success. Keep going.
+		deadline = time.Now().Add(s.interval)
+		time.Sleep(s.interval / 2)
+	}
+}
+
+// Transact runs a given function in the context of both a CockroachDB and BMDB
+// transaction, retrying as necessary.
+//
+// Most pure (meaning without side effects outside the database itself) BMDB
+// transactions should be run this way.
+func (s *Session) Transact(ctx context.Context, fn func(q *model.Queries) error) error {
+	return crdb.ExecuteTx(ctx, s.connection.db, nil, func(tx *sql.Tx) error {
+		qtx := model.New(tx)
+		sessions, err := qtx.SessionCheck(ctx, s.UUID)
+		if err != nil {
+			return fmt.Errorf("when retrieving session: %w", err)
+		}
+		if len(sessions) < 1 {
+			return ErrSessionExpired
+		}
+
+		if err := fn(qtx); err != nil {
+			return err
+		}
+
+		return nil
+	})
+}
+
+// Work runs a given function as a work item with a given process name against
+// some identified machine. Not more than one process of a given name can run
+// against a machine concurrently.
+//
+// Most impure (meaning with side effects outside the database itself) BMDB
+// transactions should be run this way.
+func (s *Session) Work(ctx context.Context, machine uuid.UUID, process model.Process, fn func() error) error {
+	err := model.New(s.connection.db).StartWork(ctx, model.StartWorkParams{
+		MachineID: machine,
+		SessionID: s.UUID,
+		Process:   process,
+	})
+	if err != nil {
+		var perr *pq.Error
+		if errors.As(err, &perr) && perr.Code == "23505" {
+			return ErrWorkConflict
+		}
+		return fmt.Errorf("could not start work: %w", err)
+	}
+	klog.Infof("Started work: %q on machine %s, session %s", process, machine, s.UUID)
+
+	defer func() {
+		err := model.New(s.connection.db).FinishWork(s.ctx, model.FinishWorkParams{
+			MachineID: machine,
+			SessionID: s.UUID,
+			Process:   process,
+		})
+		klog.Errorf("Finished work: %q on machine %s, session %s", process, machine, s.UUID)
+		if err != nil && !errors.Is(err, s.ctx.Err()) {
+			klog.Errorf("Failed to finish work: %v", err)
+			klog.Errorf("Closing session out of an abundance of caution")
+			s.ctxC()
+		}
+	}()
+
+	return fn()
+}