architecture.md

Go

• When app is started from command line, config.json is loaded and values are read from it.
• Ports and Targets are processed from the above file. Targets are processed in a way that a new struct targetServer is initialised which implements the Target interface.
• The Target interface has necessary methods needed for querying remote address information.
• To listen into every port from the config file, a new goroutine is created to setup the proxy server.
• Setup method basically resolves the local address i.e our port and starts listening to it while checking for any connections.
• To check for new connections it is run in an infinite loop and the proxy server is ran in a different goroutine.
• Loadbalancing is done using a simple roundrobin algorithm. It checks for active host and if the host is not present, it moves on to a different host i.e remote address.
• After active remote address is found, a new TCP connection is made via proxy.
• Bidirectional copy of data is done, so that client and server can both see the response sent from the remote address.

eBPF

• BPF kernel code resides in bpf/bpf_proxy_dispatch.c
• There are 2 maps defined proxy_ports of type BPF_MAP_TYPE_HASH and proxy_sock of type BPF_MAP_TYPE_SOCKMAP.
• proxy_ports map store information about the ports that are inside the config.json
• proxy_sock store the information about the fd of the proxifie's listerner socket.
• SEC contains that code that will be loaded into the memory.
• bpf_prog is the program name that get's attached to the kernel.
• port number is found by ctx->local_port and if the port is not inside the proxy_ports map the socket connection is passed forward.
• sk contains the information about proxy_sock map's 0'th element which is our fd of proxifie's listerner socket.
• bpf_sk_assign assgns the ctx to our socket sk
• Package tracer has all the information how to load eBPF program.
• Once the proxify application is run by sudo ./proxify -b. Userspace side loads the bpf ELF file bpf_proxy_dispatch.o. The function NewTracer inside pkg/tracer/tracer.go helps in achieving that.
• After that userspace loads both the maps, initialise and populate them with respective values and creates a link between network ns and eBPF program. This is done by RegisterIface function.