I am trying to get a simple client/server RPC example running between two docker containers using Golang.
When I run them on my local machine, both build and run flawlessly. I know that building them into docker containers would probably have some communication errors that I would need to work out, but I can't even get to that stage as I am getting a segmentation fault when trying to run my client.
When I run the master (server) container, it works, no problems. But when I run the worker (client) I get this:
panic: runtime error: invalid memory address or nil pointer ` `dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x10
pc=0x72425d]
goroutine 1 [running]:
net/rpc.(*Client).send(0x0, 0xc0000d61e0)
/usr/local/go/src/net/rpc/client.go:72 +0x3d
net/rpc.(*Client).Go(0x0, 0x7e062d, 0xa, 0x7887e0,
0xc0000b04a8, 0x788860, 0xb0c440, 0xc0000aa300,
0xc0000d6190)
/usr/local/go/src/net/rpc/client.go:316 +0xcc
net/rpc.(*Client).Call(...)
/usr/local/go/src/net/rpc/client.go:322
main.main()
/app/worker.go:20 +0x11c
exit status 2
My master.go:
package main
import (
"fmt"
"net"
"net/http"
"net/rpc"
)
type Args struct {
Addthis int
}
type Reply struct {
Ret int
}
type Api int
func (master *Api) Add(args Args, reply *Reply) error {
out := args.Addthis + 10
reply.Ret = out
return nil
}
func main() {
var master = new(Api)
rpc.Register(master)
rpc.HandleHTTP()
listener, _ := net.Listen("tcp", ":4040")
fmt.Printf("\nServing on %d\n", 4040)
http.Serve(listener, nil)
}
My Master Dockerfile:
FROM golang:latest
WORKDIR /app
COPY ./ /app
EXPOSE 4040
ENTRYPOINT go run master.go
I build and run master with:
docker build -t master
docker run --net=testnet --name=master master
This works fine.
My worker.go
package main
import (
"fmt"
"net/rpc"
)
type Args struct {
Addthis int
}
type Reply struct {
Ret int
}
func main() {
var reply Reply
client, _ := rpc.DialHTTP("tcp", ":4040")
num := Args{215}
client.Call("master.Add", num, &reply)
fmt.Println("Here")
fmt.Printf("\nGot back: %d\n", reply.Ret)
}
My worker Dockerfile:
FROM golang:latest
WORKDIR /app
COPY ./ /app
EXPOSE 4040
ENTRYPOINT go run worker.go
I build and run the worker with:
docker build -t worker .
docker run --net=testnet --name=worker worker
THAT'S when I get the above error.
Googling for three hours and nothing helpful seems to come up. I guess I don't know what search to use.
I know that this probably won't actually communicate as-is, but I would like to debug the communication issues, not deal with segmentation faults. The code was supplied by my professor, not as part of an assignment, but just because I asked for it. He claims this works without issue for him, and wasn't helpful with my troubleshooting (I don't think he actually tried deploying it in a container, but I'm not gonna call him out on it. He's "touchy"). "Try stack exchange!" was all he said, really.
