// preparedQueryExecute executes a prepared query.
func (s *HTTPServer) preparedQueryExecute(id string, resp http.ResponseWriter, req *http.Request) (interface{}, error) {
args := structs.PreparedQueryExecuteRequest{
QueryIDOrName: id,
}
s.parseSource(req, &args.Source)
if done := s.parse(resp, req, &args.Datacenter, &args.QueryOptions); done {
return nil, nil
}
if err := parseLimit(req, &args.Limit); err != nil {
return nil, fmt.Errorf("Bad limit: %s", err)
}
var reply structs.PreparedQueryExecuteResponse
endpoint := s.agent.getEndpoint(preparedQueryEndpoint)
if err := s.agent.RPC(endpoint+".Execute", &args, &reply); err != nil {
// We have to check the string since the RPC sheds
// the specific error type.
if err.Error() == consul.ErrQueryNotFound.Error() {
resp.WriteHeader(404)
resp.Write([]byte(err.Error()))
return nil, nil
}
return nil, err
}
// Use empty list instead of nil.
if reply.Nodes == nil {
reply.Nodes = make(structs.CheckServiceNodes, 0)
}
return reply, nil
}
// ExecuteRemote is used when a local node doesn't have any instances of a
// service available and needs to probe remote DCs. This sends the full query
// over since the remote side won't have it in its state store, and this doesn't
// do the failover logic since that's already being run on the originating DC.
// We don't want things to fan out further than one level.
func (p *PreparedQuery) ExecuteRemote(args *structs.PreparedQueryExecuteRemoteRequest,
reply *structs.PreparedQueryExecuteResponse) error {
if done, err := p.srv.forward("PreparedQuery.ExecuteRemote", args, args, reply); done {
return err
}
defer metrics.MeasureSince([]string{"consul", "prepared-query", "execute_remote"}, time.Now())
// We have to do this ourselves since we are not doing a blocking RPC.
p.srv.setQueryMeta(&reply.QueryMeta)
if args.RequireConsistent {
if err := p.srv.consistentRead(); err != nil {
return err
}
}
// Run the query locally to see what we can find.
if err := p.execute(&args.Query, reply); err != nil {
return err
}
// We don't bother trying to do an RTT sort here since we are by
// definition in another DC. We just shuffle to make sure that we
// balance the load across the results.
reply.Nodes.Shuffle()
// Apply the limit if given.
if args.Limit > 0 && len(reply.Nodes) > args.Limit {
reply.Nodes = reply.Nodes[:args.Limit]
}
return nil
}
// Execute runs a prepared query and returns the results. This will perform the
// failover logic if no local results are available. This is typically called as
// part of a DNS lookup, or when executing prepared queries from the HTTP API.
func (p *PreparedQuery) Execute(args *structs.PreparedQueryExecuteRequest,
reply *structs.PreparedQueryExecuteResponse) error {
if done, err := p.srv.forward("PreparedQuery.Execute", args, args, reply); done {
return err
}
defer metrics.MeasureSince([]string{"consul", "prepared-query", "execute"}, time.Now())
// We have to do this ourselves since we are not doing a blocking RPC.
p.srv.setQueryMeta(&reply.QueryMeta)
if args.RequireConsistent {
if err := p.srv.consistentRead(); err != nil {
return err
}
}
// Try to locate the query.
state := p.srv.fsm.State()
_, query, err := state.PreparedQueryLookup(args.QueryIDOrName)
if err != nil {
return err
}
if query == nil {
return ErrQueryNotFound
}
// Execute the query for the local DC.
if err := p.execute(query, reply); err != nil {
return err
}
// Shuffle the results in case coordinates are not available if they
// requested an RTT sort.
reply.Nodes.Shuffle()
if err := p.srv.sortNodesByDistanceFrom(args.Source, reply.Nodes); err != nil {
return err
}
// Apply the limit if given.
if args.Limit > 0 && len(reply.Nodes) > args.Limit {
reply.Nodes = reply.Nodes[:args.Limit]
}
// In the happy path where we found some healthy nodes we go with that
// and bail out. Otherwise, we fail over and try remote DCs, as allowed
// by the query setup.
if len(reply.Nodes) == 0 {
wrapper := &queryServerWrapper{p.srv}
if err := queryFailover(wrapper, query, args.Limit, args.QueryOptions, reply); err != nil {
return err
}
}
return nil
}
// execute runs a prepared query in the local DC without any failover. We don't
// apply any sorting options at this level - it should be done up above.
func (p *PreparedQuery) execute(query *structs.PreparedQuery,
reply *structs.PreparedQueryExecuteResponse) error {
state := p.srv.fsm.State()
_, nodes, err := state.CheckServiceNodes(query.Service.Service)
if err != nil {
return err
}
// This is kind of a paranoia ACL check, in case something changed with
// the token from the time the query was registered. Note that we use
// the token stored with the query, NOT the passed-in one, which is
// critical to how queries work (the query becomes a proxy for a lookup
// using the ACL it was created with).
acl, err := p.srv.resolveToken(query.Token)
if err != nil {
return err
}
if acl != nil && !acl.ServiceRead(query.Service.Service) {
p.srv.logger.Printf("[WARN] consul.prepared_query: Execute of prepared query for service '%s' denied due to ACLs", query.Service.Service)
return permissionDeniedErr
}
// Filter out any unhealthy nodes.
nodes = nodes.Filter(query.Service.OnlyPassing)
// Apply the tag filters, if any.
if len(query.Service.Tags) > 0 {
nodes = tagFilter(query.Service.Tags, nodes)
}
// Capture the nodes and pass the DNS information through to the reply.
reply.Service = query.Service.Service
reply.Nodes = nodes
reply.DNS = query.DNS
// Stamp the result for this datacenter.
reply.Datacenter = p.srv.config.Datacenter
return nil
}
// queryFailover runs an algorithm to determine which DCs to try and then calls
// them to try to locate alternative services.
func queryFailover(q queryServer, query *structs.PreparedQuery,
limit int, options structs.QueryOptions,
reply *structs.PreparedQueryExecuteResponse) error {
// Pull the list of other DCs. This is sorted by RTT in case the user
// has selected that.
nearest, err := q.GetOtherDatacentersByDistance()
if err != nil {
return err
}
// This will help us filter unknown DCs supplied by the user.
known := make(map[string]struct{})
for _, dc := range nearest {
known[dc] = struct{}{}
}
// Build a candidate list of DCs to try, starting with the nearest N
// from RTTs.
var dcs []string
index := make(map[string]struct{})
if query.Service.Failover.NearestN > 0 {
for i, dc := range nearest {
if !(i < query.Service.Failover.NearestN) {
break
}
dcs = append(dcs, dc)
index[dc] = struct{}{}
}
}
// Then add any DCs explicitly listed that weren't selected above.
for _, dc := range query.Service.Failover.Datacenters {
// This will prevent a log of other log spammage if we do not
// attempt to talk to datacenters we don't know about.
if _, ok := known[dc]; !ok {
q.GetLogger().Printf("[DEBUG] consul.prepared_query: Skipping unknown datacenter '%s' in prepared query", dc)
continue
}
// This will make sure we don't re-try something that fails
// from the NearestN list.
if _, ok := index[dc]; !ok {
dcs = append(dcs, dc)
}
}
// Now try the selected DCs in priority order.
failovers := 0
for _, dc := range dcs {
// This keeps track of how many iterations we actually run.
failovers++
// Be super paranoid and set the nodes slice to nil since it's
// the same slice we used before. We know there's nothing in
// there, but the underlying msgpack library has a policy of
// updating the slice when it's non-nil, and that feels dirty.
// Let's just set it to nil so there's no way to communicate
// through this slice across successive RPC calls.
reply.Nodes = nil
// Note that we pass along the limit since it can be applied
// remotely to save bandwidth. We also pass along the consistency
// mode information we were given, so that applies to the remote
// query as well.
remote := &structs.PreparedQueryExecuteRemoteRequest{
Datacenter: dc,
Query: *query,
Limit: limit,
QueryOptions: options,
}
if err := q.ForwardDC("PreparedQuery.ExecuteRemote", dc, remote, reply); err != nil {
q.GetLogger().Printf("[WARN] consul.prepared_query: Failed querying for service '%s' in datacenter '%s': %s", query.Service.Service, dc, err)
continue
}
// We can stop if we found some nodes.
if len(reply.Nodes) > 0 {
break
}
}
// Set this at the end because the response from the remote doesn't have
// this information.
reply.Failovers = failovers
return nil
}