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Diffstat (limited to 'src/core/ext/filters/client_channel/README.md')
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diff --git a/src/core/ext/filters/client_channel/README.md b/src/core/ext/filters/client_channel/README.md new file mode 100644 index 0000000000..7c209db12e --- /dev/null +++ b/src/core/ext/filters/client_channel/README.md @@ -0,0 +1,65 @@ +Client Configuration Support for GRPC +===================================== + +This library provides high level configuration machinery to construct client +channels and load balance between them. + +Each grpc_channel is created with a grpc_resolver. It is the resolver's duty +to resolve a name into a set of arguments for the channel. Such arguments +might include: + +- a list of (ip, port) addresses to connect to +- a load balancing policy to decide which server to send a request to +- a set of filters to mutate outgoing requests (say, by adding metadata) + +The resolver provides this data as a stream of grpc_channel_args objects to +the channel. We represent arguments as a stream so that they can be changed +by the resolver during execution, by reacting to external events (such as +new service configuration data being pushed to some store). + + +Load Balancing +-------------- + +Load balancing configuration is provided by a grpc_lb_policy object. + +The primary job of the load balancing policies is to pick a target server +given only the initial metadata for a request. It does this by providing +a grpc_subchannel object to the owning channel. + + +Sub-Channels +------------ + +A sub-channel provides a connection to a server for a client channel. It has a +connectivity state like a regular channel, and so can be connected or +disconnected. This connectivity state can be used to inform load balancing +decisions (for example, by avoiding disconnected backends). + +Configured sub-channels are fully setup to participate in the grpc data plane. +Their behavior is specified by a set of grpc channel filters defined at their +construction. To customize this behavior, resolvers build +grpc_client_channel_factory objects, which use the decorator pattern to customize +construction arguments for concrete grpc_subchannel instances. + + +Naming for GRPC +=============== + +Names in GRPC are represented by a URI (as defined in +[RFC 3986](https://tools.ietf.org/html/rfc3986)). + +The following schemes are currently supported: + +dns:///host:port - dns schemes are currently supported so long as authority is + empty (authority based dns resolution is expected in a future + release) + +unix:path - the unix scheme is used to create and connect to unix domain + sockets - the authority must be empty, and the path + represents the absolute or relative path to the desired + socket + +ipv4:host:port - a pre-resolved ipv4 dotted decimal address/port combination + +ipv6:[host]:port - a pre-resolved ipv6 address/port combination |