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feat: Configure connections using DNS domain names (#843)
The dialer may be configured to use a DNS name to look up the instance
name instead of configuring the connector with the instance name directly.
Add a DNS TXT record for the Cloud SQL instance to a private DNS server
or a private Google Cloud DNS Zone used by your application. For example:
- Record type: TXT
- Name: `prod-db.mycompany.example.com` – This is the domain name used by the application
- Value: `my-project:region:my-instance` – This is the instance connection name
Configure the dialer with the cloudsqlconn.WithDNSResolver() option.
Open a database connection using the DNS name:
```
db, err := sql.Open(
"cloudsql-mysql",
"myuser:mypass@cloudsql-mysql(prod-db.mycompany.example.com)/mydb",
)
```
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,123 @@ | ||
| // Copyright 2024 Google LLC | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 (the "License"); | ||
| // you may not use this file except in compliance with the License. | ||
| // You may obtain a copy of the License at | ||
| // | ||
| // https://www.apache.org/licenses/LICENSE-2.0 | ||
| // | ||
| // Unless required by applicable law or agreed to in writing, software | ||
| // distributed under the License is distributed on an "AS IS" BASIS, | ||
| // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
| // See the License for the specific language governing permissions and | ||
| // limitations under the License. | ||
|
|
||
| package cloudsql | ||
|
|
||
| import ( | ||
| "context" | ||
| "fmt" | ||
| "net" | ||
| "sort" | ||
|
|
||
| "cloud.google.com/go/cloudsqlconn/instance" | ||
| ) | ||
|
|
||
| // DNSResolver uses the default net.Resolver to find | ||
| // TXT records containing an instance name for a DNS record. | ||
| var DNSResolver = &DNSInstanceConnectionNameResolver{ | ||
| dnsResolver: net.DefaultResolver, | ||
| } | ||
|
|
||
| // DefaultResolver simply parses instance names. | ||
| var DefaultResolver = &ConnNameResolver{} | ||
|
|
||
| // ConnNameResolver simply parses instance names. Implements | ||
| // InstanceConnectionNameResolver | ||
| type ConnNameResolver struct { | ||
| } | ||
|
|
||
| // Resolve returns the instance name, possibly using DNS. This will return an | ||
| // instance.ConnName or an error if it was unable to resolve an instance name. | ||
| func (r *ConnNameResolver) Resolve(_ context.Context, icn string) (instanceName instance.ConnName, err error) { | ||
| return instance.ParseConnName(icn) | ||
| } | ||
|
|
||
| // netResolver groups the methods on net.Resolver that are used by the DNS | ||
| // resolver implementation. This allows an application to replace the default | ||
| // net.DefaultResolver with a custom implementation. For example: the | ||
| // application may need to connect to a specific DNS server using a specially | ||
| // configured instance of net.Resolver. | ||
| type netResolver interface { | ||
| LookupTXT(ctx context.Context, name string) ([]string, error) | ||
| } | ||
|
|
||
| // DNSInstanceConnectionNameResolver can resolve domain names into instance names using | ||
| // TXT records in DNS. Implements InstanceConnectionNameResolver | ||
| type DNSInstanceConnectionNameResolver struct { | ||
| dnsResolver netResolver | ||
| } | ||
|
|
||
| // Resolve returns the instance name, possibly using DNS. This will return an | ||
| // instance.ConnName or an error if it was unable to resolve an instance name. | ||
| func (r *DNSInstanceConnectionNameResolver) Resolve(ctx context.Context, icn string) (instanceName instance.ConnName, err error) { | ||
| cn, err := instance.ParseConnName(icn) | ||
| if err != nil { | ||
| // The connection name was not project:region:instance | ||
| // Attempt to query a TXT record and see if it works instead. | ||
| cn, err = r.queryDNS(ctx, icn) | ||
| if err != nil { | ||
| return instance.ConnName{}, err | ||
| } | ||
| } | ||
|
|
||
| return cn, nil | ||
| } | ||
|
|
||
| // queryDNS attempts to resolve a TXT record for the domain name. | ||
| // The DNS TXT record's target field is used as instance name. | ||
| // | ||
| // This handles several conditions where the DNS records may be missing or | ||
| // invalid: | ||
| // - The domain name resolves to 0 DNS records - return an error | ||
| // - Some DNS records to not contain a well-formed instance name - return the | ||
| // first well-formed instance name. If none found return an error. | ||
| // - The domain name resolves to 2 or more DNS record - return first valid | ||
| // record when sorted by priority: lowest value first, then by target: | ||
| // alphabetically. | ||
| func (r *DNSInstanceConnectionNameResolver) queryDNS(ctx context.Context, domainName string) (instance.ConnName, error) { | ||
| // Attempt to query the TXT records. | ||
| // This could return a partial error where both err != nil && len(records) > 0. | ||
| records, err := r.dnsResolver.LookupTXT(ctx, domainName) | ||
| // If resolve failed and no records were found, return the error. | ||
| if err != nil { | ||
| return instance.ConnName{}, fmt.Errorf("unable to resolve TXT record for %q: %v", domainName, err) | ||
| } | ||
|
|
||
| // Process the records returning the first valid TXT record. | ||
|
|
||
| // Sort the TXT record values alphabetically by instance name | ||
| sort.Slice(records, func(i, j int) bool { | ||
| return records[i] < records[j] | ||
| }) | ||
|
|
||
| var perr error | ||
| // Attempt to parse records, returning the first valid record. | ||
| for _, record := range records { | ||
| // Parse the target as a CN | ||
| cn, parseErr := instance.ParseConnName(record) | ||
| if parseErr != nil { | ||
| perr = fmt.Errorf("unable to parse TXT for %q -> %q : %v", domainName, record, parseErr) | ||
| continue | ||
| } | ||
| return cn, nil | ||
| } | ||
|
|
||
| // If all the records failed to parse, return one of the parse errors | ||
| if perr != nil { | ||
| return instance.ConnName{}, perr | ||
| } | ||
|
|
||
| // No records were found, return an error. | ||
| return instance.ConnName{}, fmt.Errorf("no valid TXT records found for %q", domainName) | ||
| } |
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