mirror of https://github.com/grpc/grpc.git
The C based gRPC (C++, Python, Ruby, Objective-C, PHP, C#)
https://grpc.io/
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
85 lines
3.7 KiB
85 lines
3.7 KiB
# gRPC Name Resolution |
|
|
|
## Overview |
|
|
|
gRPC supports DNS as the default name-system. A number of alternative |
|
name-systems are used in various deployments. We support an API that is |
|
general enough to support a range of name-systems and the corresponding |
|
syntax for names. The gRPC client library in various languages will |
|
provide a plugin mechanism so resolvers for different name-systems can |
|
be plugged in. |
|
|
|
## Detailed Design |
|
|
|
### Name Syntax |
|
|
|
A fully qualified, self contained name used for gRPC channel construction |
|
uses URI syntax as defined in [RFC 3986](https://tools.ietf.org/html/rfc3986). |
|
|
|
The URI scheme indicates what resolver plugin to use. If no scheme |
|
prefix is specified or the scheme is unknown, the `dns` scheme is used |
|
by default. |
|
|
|
The URI path indicates the name to be resolved. |
|
|
|
Most gRPC implementations support the following URI schemes: |
|
|
|
- `dns:[//authority/]host[:port]` -- DNS (default) |
|
- `host` is the host to resolve via DNS. |
|
- `port` is the port to return for each address. If not specified, |
|
443 is used (but some implementations default to 80 for insecure |
|
channels). |
|
- `authority` indicates the DNS server to use, although this is only |
|
supported by some implementations. (In C-core, the default DNS |
|
resolver does not support this, but the c-ares based resolver |
|
supports specifying this in the form "IP:port".) |
|
|
|
- `unix:path`, `unix://absolute_path` -- Unix domain sockets (Unix systems only) |
|
- `path` indicates the location of the desired socket. |
|
- In the first form, the path may be relative or absolute; in the |
|
second form, the path must be absolute (i.e., there will actually be |
|
three slashes, two prior to the path and another to begin the |
|
absolute path). |
|
|
|
- `unix-abstract:abstract_path` -- Unix domain socket in abstract namespace (Unix systems only) |
|
- `abstract_path` indicates a name in the abstract namespace. |
|
- The name has no connection with filesystem pathnames. |
|
- No permissions will apply to the socket - any process/user may access the socket. |
|
- The underlying implementation of Abstract sockets uses a null byte ('\0') |
|
as the first character; the implementation will prepend this null. Do not include |
|
the null in `abstract_path`. |
|
|
|
The following schemes are supported by the gRPC C-core implementation, |
|
but may not be supported in other languages: |
|
|
|
- `ipv4:address[:port][,address[:port],...]` -- IPv4 addresses |
|
- Can specify multiple comma-delimited addresses of the form `address[:port]`: |
|
- `address` is the IPv4 address to use. |
|
- `port` is the port to use. If not specified, 443 is used. |
|
|
|
- `ipv6:address[:port][,address[:port],...]` -- IPv6 addresses |
|
- Can specify multiple comma-delimited addresses of the form `address[:port]`: |
|
- `address` is the IPv6 address to use. To use with a `port` the `address` |
|
must enclosed in literal square brackets (`[` and `]`). Example: |
|
`ipv6:[2607:f8b0:400e:c00::ef]:443` or `ipv6:[::]:1234` |
|
- `port` is the port to use. If not specified, 443 is used. |
|
|
|
In the future, additional schemes such as `etcd` could be added. |
|
|
|
### Resolver Plugins |
|
|
|
The gRPC client library will use the specified scheme to pick the right |
|
resolver plugin and pass it the fully qualified name string. |
|
|
|
Resolvers should be able to contact the authority and get a resolution |
|
that they return back to the gRPC client library. The returned contents |
|
include: |
|
|
|
- A list of resolved addresses (both IP address and port). Each address |
|
may have a set of arbitrary attributes (key/value pairs) associated with |
|
it, which can be used to communicate information from the resolver to the |
|
[load balancing](load-balancing.md) policy. |
|
- A [service config](service_config.md). |
|
|
|
The plugin API allows the resolvers to continuously watch an endpoint |
|
and return updated resolutions as needed.
|
|
|