Challenge 4 - Production runtime

Write a service with GOMAXPROCS and memory limit set.

Challenge: a production-ready runtime

You will prepare a service's main function together with its runtime settings:

Set the memory limit to 90% of the container limit (debug.SetMemoryLimit).
Set GOMAXPROCS from the CPU quota.
Log the version, GOMAXPROCS and memory limit at startup.
Shut down gracefully on SIGTERM.

limit := int64(float64(konteynerBayt) * 0.9)
debug.SetMemoryLimit(limit)

Make the settings testable

If you separate reading the environment and computing into a pure function, main stays thin and the logic becomes testable:

type Ayar struct {
    Procs    int
    MemLimit int64
}

func hesapla(cpuKota float64, bellek int64) Ayar {
    p := int(cpuKota)
    if p < 1 { p = 1 }
    return Ayar{Procs: p, MemLimit: int64(float64(bellek) * 0.9)}
}

Exercise Settings computation

Write the Ayar type and the hesapla function above. Print the results of hesapla(0.5, 1000) and hesapla(4, 1000) with %+v on separate lines.

Show example solution

package main

import "fmt"

type Ayar struct {
    Procs    int
    MemLimit int64
}

func hesapla(cpuKota float64, bellek int64) Ayar {
    p := int(cpuKota)
    if p < 1 {
        p = 1
    }
    return Ayar{Procs: p, MemLimit: int64(float64(bellek) * 0.9)}
}

func main() {
    fmt.Printf("%+v\n", hesapla(0.5, 1000))
    fmt.Printf("%+v\n", hesapla(4, 1000))
}

Test yourself

Why set the memory limit to 90% of the container limit instead of all of it?
- So GC runs less often
- Because Go doesn't accept 100%
- It makes no difference
- To leave room for stacks and non-Go memory and avoid OOM
Show answer

To leave room for stacks and non-Go memory and avoid OOM — GOMEMLIMIT is a soft limit and can't fully track some memory such as cgo or mmap; leaving headroom keeps the kernel from killing the process.

Apply the limit

a := hesapla(2, 512<<20)
runtime.GOMAXPROCS(a.Procs)
debug.____(a.MemLimit)

Show answer

a := hesapla(2, 512<<20)
runtime.GOMAXPROCS(a.Procs)
debug.SetMemoryLimit(a.MemLimit)

Setting and reason

GOMAXPROCS = kota

Avoids CPU throttling
GOMEMLIMIT = %90

Avoids OOM
Startup log

Easier diagnosis
Handling SIGTERM

Graceful shutdown

Next lesson: Expert section exam

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