open-consul/agent/consul/snapshot_endpoint.go

251 lines
7.6 KiB
Go

// The snapshot endpoint is a special non-RPC endpoint that supports streaming
// for taking and restoring snapshots for disaster recovery. This gets wired
// directly into Consul's stream handler, and a new TCP connection is made for
// each request.
//
// This also includes a SnapshotRPC() function, which acts as a lightweight
// client that knows the details of the stream protocol.
package consul
import (
"bytes"
"errors"
"fmt"
"io"
"io/ioutil"
"net"
"time"
"github.com/hashicorp/consul/acl"
"github.com/hashicorp/consul/agent/pool"
"github.com/hashicorp/consul/agent/structs"
"github.com/hashicorp/consul/snapshot"
"github.com/hashicorp/go-msgpack/codec"
)
// dispatchSnapshotRequest takes an incoming request structure with possibly some
// streaming data (for a restore) and returns possibly some streaming data (for
// a snapshot save). We can't use the normal RPC mechanism in a streaming manner
// like this, so we have to dispatch these by hand.
func (s *Server) dispatchSnapshotRequest(args *structs.SnapshotRequest, in io.Reader,
reply *structs.SnapshotResponse) (io.ReadCloser, error) {
// Perform DC forwarding.
if dc := args.Datacenter; dc != s.config.Datacenter {
manager, server, ok := s.router.FindRoute(dc)
if !ok {
return nil, structs.ErrNoDCPath
}
snap, err := SnapshotRPC(s.connPool, dc, server.ShortName, server.Addr, args, in, reply)
if err != nil {
manager.NotifyFailedServer(server)
return nil, err
}
return snap, nil
}
// Perform leader forwarding if required.
if !args.AllowStale {
if isLeader, server := s.getLeader(); !isLeader {
if server == nil {
return nil, structs.ErrNoLeader
}
return SnapshotRPC(s.connPool, args.Datacenter, server.ShortName, server.Addr, args, in, reply)
}
}
// Verify token is allowed to operate on snapshots. There's only a
// single ACL sense here (not read and write) since reading gets you
// all the ACLs and you could escalate from there.
if rule, err := s.ResolveToken(args.Token); err != nil {
return nil, err
} else if rule != nil && rule.Snapshot(nil) != acl.Allow {
return nil, acl.ErrPermissionDenied
}
// Dispatch the operation.
switch args.Op {
case structs.SnapshotSave:
if !args.AllowStale {
if err := s.consistentRead(); err != nil {
return nil, err
}
}
// Set the metadata here before we do anything; this should always be
// pessimistic if we get more data while the snapshot is being taken.
s.setQueryMeta(&reply.QueryMeta)
// Take the snapshot and capture the index.
snap, err := snapshot.New(s.logger, s.raft)
reply.Index = snap.Index()
return snap, err
case structs.SnapshotRestore:
if args.AllowStale {
return nil, fmt.Errorf("stale not allowed for restore")
}
// Restore the snapshot.
if err := snapshot.Restore(s.logger, in, s.raft); err != nil {
return nil, err
}
// Run a barrier so we are sure that our FSM is caught up with
// any snapshot restore details (it's also part of Raft's restore
// process but we don't want to depend on that detail for this to
// be correct). Once that works, we can redo the leader actions
// so our leader-maintained state will be up to date.
barrier := s.raft.Barrier(0)
if err := barrier.Error(); err != nil {
return nil, err
}
// This'll be used for feedback from the leader loop.
errCh := make(chan error, 1)
timeoutCh := time.After(time.Minute)
select {
// Tell the leader loop to reassert leader actions since we just
// replaced the state store contents.
case s.reassertLeaderCh <- errCh:
// We might have lost leadership while waiting to kick the loop.
case <-timeoutCh:
return nil, fmt.Errorf("timed out waiting to re-run leader actions")
// Make sure we don't get stuck during shutdown
case <-s.shutdownCh:
}
select {
// Wait for the leader loop to finish up.
case err := <-errCh:
if err != nil {
return nil, err
}
// We might have lost leadership while the loop was doing its
// thing.
case <-timeoutCh:
return nil, fmt.Errorf("timed out waiting for re-run of leader actions")
// Make sure we don't get stuck during shutdown
case <-s.shutdownCh:
}
// Give the caller back an empty reader since there's nothing to
// stream back.
return ioutil.NopCloser(bytes.NewReader([]byte(""))), nil
default:
return nil, fmt.Errorf("unrecognized snapshot op %q", args.Op)
}
}
// handleSnapshotRequest reads the request from the conn and dispatches it. This
// will be called from a goroutine after an incoming stream is determined to be
// a snapshot request.
func (s *Server) handleSnapshotRequest(conn net.Conn) error {
var args structs.SnapshotRequest
dec := codec.NewDecoder(conn, structs.MsgpackHandle)
if err := dec.Decode(&args); err != nil {
return fmt.Errorf("failed to decode request: %v", err)
}
var reply structs.SnapshotResponse
snap, err := s.dispatchSnapshotRequest(&args, conn, &reply)
if err != nil {
reply.Error = err.Error()
goto RESPOND
}
defer func() {
if err := snap.Close(); err != nil {
s.logger.Error("Failed to close snapshot", "error", err)
}
}()
RESPOND:
enc := codec.NewEncoder(conn, structs.MsgpackHandle)
if err := enc.Encode(&reply); err != nil {
return fmt.Errorf("failed to encode response: %v", err)
}
if snap != nil {
if _, err := io.Copy(conn, snap); err != nil {
return fmt.Errorf("failed to stream snapshot: %v", err)
}
}
return nil
}
// SnapshotRPC is a streaming client function for performing a snapshot RPC
// request to a remote server. It will create a fresh connection for each
// request, send the request header, and then stream in any data from the
// reader (for a restore). It will then parse the received response header, and
// if there's no error will return an io.ReadCloser (that you must close) with
// the streaming output (for a snapshot). If the reply contains an error, this
// will always return an error as well, so you don't need to check the error
// inside the filled-in reply.
func SnapshotRPC(
connPool *pool.ConnPool,
dc string,
nodeName string,
addr net.Addr,
args *structs.SnapshotRequest,
in io.Reader,
reply *structs.SnapshotResponse,
) (io.ReadCloser, error) {
// Write the snapshot RPC byte to set the mode, then perform the
// request.
conn, hc, err := connPool.DialTimeout(dc, nodeName, addr, pool.RPCSnapshot)
if err != nil {
return nil, err
}
// keep will disarm the defer on success if we are returning the caller
// our connection to stream the output.
var keep bool
defer func() {
if !keep {
conn.Close()
}
}()
// Push the header encoded as msgpack, then stream the input.
enc := codec.NewEncoder(conn, structs.MsgpackHandle)
if err := enc.Encode(&args); err != nil {
return nil, fmt.Errorf("failed to encode request: %v", err)
}
if _, err := io.Copy(conn, in); err != nil {
return nil, fmt.Errorf("failed to copy snapshot in: %v", err)
}
// Our RPC protocol requires support for a half-close in order to signal
// the other side that they are done reading the stream, since we don't
// know the size in advance. This saves us from having to buffer just to
// calculate the size.
if hc != nil {
if err := hc.CloseWrite(); err != nil {
return nil, fmt.Errorf("failed to half close snapshot connection: %v", err)
}
} else {
return nil, fmt.Errorf("snapshot connection requires half-close support")
}
// Pull the header decoded as msgpack. The caller can continue to read
// the conn to stream the remaining data.
dec := codec.NewDecoder(conn, structs.MsgpackHandle)
if err := dec.Decode(reply); err != nil {
return nil, fmt.Errorf("failed to decode response: %v", err)
}
if reply.Error != "" {
return nil, errors.New(reply.Error)
}
keep = true
return conn, nil
}