Ketahanan dalam komunikasi antara perkhidmatan mikro menggunakan failsafe-go lib

Mari kita mulakan pada permulaan. Apakah daya tahan? Saya suka definisi dalam siaran ini:

Keupayaan intrinsik sistem untuk melaraskan fungsinya sebelum, semasa, atau selepas perubahan dan gangguan, supaya ia dapat mengekalkan operasi yang diperlukan di bawah kedua-dua keadaan yang dijangka dan tidak dijangka

Memandangkan ia adalah istilah yang luas, saya akan menumpukan pada komunikasi antara perkhidmatan mikro dalam siaran ini. Untuk melakukan ini, saya membuat dua perkhidmatan menggunakan Go: serviceA dan serviceB (kreativiti saya tidak tinggi semasa menulis siaran ini).

Kod awal untuk kedua-duanya adalah seperti berikut:

package main

// serviceA
import (
    "encoding/json"
    "io"
    "log/slog"
    "net/http"
    "os"

    "github.com/go-chi/chi/v5"
    slogchi "github.com/samber/slog-chi"
)

func main() {
    logger := slog.New(slog.NewJSONHandler(os.Stdout, nil))
    r := chi.NewRouter()
    r.Use(slogchi.New(logger))
    r.Get("/", func(w http.ResponseWriter, r *http.Request) {
        type response struct {
            Message string `json:"message"`
        }
        resp, err := http.Get("http://localhost:3001")
        if err != nil {
            w.WriteHeader(http.StatusInternalServerError)
            w.Write([]byte(err.Error()))
            return
        }
        body, err := io.ReadAll(resp.Body)
        if err != nil {
            w.WriteHeader(http.StatusInternalServerError)
            w.Write([]byte(err.Error()))
            return
        }
        defer resp.Body.Close()
        var data response
        err = json.Unmarshal(body, &data)
        if err != nil {
            w.WriteHeader(http.StatusInternalServerError)
            w.Write([]byte(err.Error()))
            return
        }
        w.Header().Set("Content-Type", "application/json")
        w.Write([]byte(`{"messageA": "hello from service A","messageB": "` + data.Message + `"}`))
    })
    http.ListenAndServe(":3000", r)
}

package main

//serviceB
import (
    "net/http"

    "github.com/go-chi/chi/v5"
    "github.com/go-chi/chi/v5/middleware"
)

func main() {
    r := chi.NewRouter()
    r.Use(middleware.Logger)
    r.Get("/", func(w http.ResponseWriter, r *http.Request) {
        w.Header().Set("Content-Type", "application/json")
        w.Write([]byte(`{"message": "hello from service B"}`))
    })
    http.ListenAndServe(":3001", r)
}

Seperti yang anda lihat dalam kod, jika serviceB menghadapi masalah, ia akan menjejaskan fungsi serviceA, kerana ia tidak mengendalikan sebarang kegagalan komunikasi. Kami akan menambah baik perkara ini dengan menggunakan lib failsafe-go.

Menurut dokumentasi di tapak web rasmi:

Failsafe-go ialah perpustakaan untuk membina aplikasi Go yang berdaya tahan dan bertolak ansur terhadap kesalahan. Ia berfungsi dengan membungkus fungsi dengan satu atau lebih dasar daya tahan, yang boleh digabungkan dan digubah mengikut keperluan.

Mari kita mulakan dengan menggunakan beberapa dasar yang tersedia dan menguji komposisinya.

tamat masa

Dasar pertama yang akan kami uji adalah yang paling mudah, termasuk tamat masa untuk memastikan sambungan terputus jika serviceB mengambil masa terlalu lama untuk bertindak balas dan pelanggan tahu sebabnya.

Langkah pertama ialah menukar perkhidmatanB supaya ia termasuk kelewatan untuk memudahkan untuk menunjukkan senario:

package main
//serviceB
import (
    "net/http"
    "time"

    "github.com/go-chi/chi/v5"
    "github.com/go-chi/chi/v5/middleware"
)

func main() {
    r := chi.NewRouter()
    r.Use(middleware.Logger)
    r.Get("/", func(w http.ResponseWriter, r *http.Request) {
        time.Sleep(5 * time.Second) //add a delay to simulate a slow service
        w.Header().Set("Content-Type", "application/json")
        w.Write([]byte(`{"message": "hello from service B"}`))
    })
    http.ListenAndServe(":3001", r)
}

Selepas memasang failsafe-go, gunakan arahan:

❯ cd serviceA
❯ go get github.com/failsafe-go/failsafe-go

Kod serviceA/main.go ialah:

package main

import (
    "encoding/json"
    "io"
    "log/slog"
    "net/http"
    "os"
    "time"

    "github.com/failsafe-go/failsafe-go"
    "github.com/failsafe-go/failsafe-go/failsafehttp"
    "github.com/failsafe-go/failsafe-go/timeout"
    "github.com/go-chi/chi/v5"
    slogchi "github.com/samber/slog-chi"
)

func main() {
    logger := slog.New(slog.NewJSONHandler(os.Stdout, nil))
    r := chi.NewRouter()
    r.Use(slogchi.New(logger))
    r.Get("/", func(w http.ResponseWriter, r *http.Request) {
        type response struct {
            Message string `json:"message"`
        }
        // Create a Timeout for 1 second
        timeout := newTimeout(logger)

        // Use the Timeout with a failsafe RoundTripper
        roundTripper := failsafehttp.NewRoundTripper(nil, timeout)
        client := &http.Client{Transport: roundTripper}
        resp, err := client.Get("http://localhost:3001")
        if err != nil {
            w.WriteHeader(http.StatusInternalServerError)
            w.Write([]byte(err.Error()))
            return
        }
        body, err := io.ReadAll(resp.Body)
        if err != nil {
            w.WriteHeader(http.StatusInternalServerError)
            w.Write([]byte(err.Error()))
            return
        }
        defer resp.Body.Close()
        var data response
        err = json.Unmarshal(body, &data)
        if err != nil {
            w.WriteHeader(http.StatusInternalServerError)
            w.Write([]byte(err.Error()))
            return
        }
        w.Header().Set("Content-Type", "application/json")
        w.Write([]byte(`{"messageA": "hello from service A","messageB": "` + data.Message + `"}`))
    })
    http.ListenAndServe(":3000", r)
}

func newTimeout(logger *slog.Logger) timeout.Timeout[*http.Response] {
    return timeout.Builder[*http.Response](1 * time.Second).
        OnTimeoutExceeded(func(e failsafe.ExecutionDoneEvent[*http.Response]) {
            logger.Info("Connection timed out")
        }).Build()
}

Untuk menguji cara ia berfungsi, saya menggunakan curl untuk mengakses perkhidmatanA:

❯ curl -v http://localhost:3000
* Host localhost:3000 was resolved.
* IPv6: ::1
* IPv4: 127.0.0.1
*   Trying [::1]:3000...
* Connected to localhost (::1) port 3000
> GET / HTTP/1.1
> Host: localhost:3000
> User-Agent: curl/8.7.1
> Accept: */*
>
* Request completely sent off
< HTTP/1.1 500 Internal Server Error
< Date: Fri, 23 Aug 2024 19:43:23 GMT
< Content-Length: 45
< Content-Type: text/plain; charset=utf-8
<
* Connection #0 to host localhost left intact
Get "http://localhost:3001": timeout exceeded⏎

Dan output berikut dijana oleh serviceA:

go run main.go
{"time":"2024-08-20T08:37:36.852886-03:00","level":"INFO","msg":"Connection timed out"}
{"time":"2024-08-20T08:37:36.856079-03:00","level":"ERROR","msg":"500: Internal Server Error","request":{"time":"2024-08-20T08:37:35.851262-03:00","method":"GET","host":"localhost:3000","path":"/","query":"","params":{},"route":"/","ip":"[::1]:63409","referer":"","length":0},"response":{"time":"2024-08-20T08:37:36.856046-03:00","latency":1004819000,"status":500,"length":45},"id":""}

Dengan cara ini, adalah mungkin untuk melihat bahawa pelanggan (keriting dalam kes ini) mempunyai tindak balas yang berkesan dan perkhidmatanA tidak memberi kesan yang ketara.

Mari kita tingkatkan daya tahan aplikasi kita dengan menyiasat dasar lain yang bermanfaat: cuba semula.

Cuba semula

Sekali lagi, adalah perlu untuk membuat perubahan kepada serviceB untuk menambah ralat rawak:

package main

import (
    "math/rand"
    "net/http"
    "strconv"
    "time"

    "github.com/go-chi/chi/v5"
    "github.com/go-chi/chi/v5/middleware"
)

func main() {
    r := chi.NewRouter()
    r.Use(middleware.Logger)
    r.Get("/", func(w http.ResponseWriter, r *http.Request) {
        retryAfterDelay := 1 * time.Second
        if fail() {
            w.Header().Add("Retry-After", strconv.Itoa(int(retryAfterDelay.Seconds())))
            w.WriteHeader(http.StatusServiceUnavailable)
            return
        }
        w.Header().Set("Content-Type", "application/json")
        w.Write([]byte(`{"message": "hello from service B"}`))
    })
    http.ListenAndServe(":3001", r)
}

func fail() bool {
    if flipint := rand.Intn(2); flipint == 0 {
        return true
    }
    return false
}

Untuk memudahkan pemahaman, saya menunjukkan satu dasar pada satu masa, itulah sebabnya serviceA ditukar kepada versi asal dan bukan kepada versi dengan tamat masa. Kemudian, kami akan mengkaji cara untuk mengarang beberapa dasar untuk menjadikan aplikasi lebih berdaya tahan.

Kod serviceA/main.go kelihatan seperti ini:

package main

import (
    "encoding/json"
    "fmt"
    "io"
    "log/slog"
    "net/http"
    "os"
    "time"

    "github.com/failsafe-go/failsafe-go"
    "github.com/failsafe-go/failsafe-go/failsafehttp"
    "github.com/failsafe-go/failsafe-go/retrypolicy"
    "github.com/go-chi/chi/v5"
    slogchi "github.com/samber/slog-chi"
)

func main() {
    logger := slog.New(slog.NewJSONHandler(os.Stdout, nil))
    r := chi.NewRouter()
    r.Use(slogchi.New(logger))
    r.Get("/", func(w http.ResponseWriter, r *http.Request) {
        type response struct {
            Message string `json:"message"`
        }
        // Create a RetryPolicy that only handles 500 responses, with backoff delays between retries
        retryPolicy := newRetryPolicy(logger)

        // Use the RetryPolicy with a failsafe RoundTripper
        roundTripper := failsafehttp.NewRoundTripper(nil, retryPolicy)
        client := &http.Client{Transport: roundTripper}

        resp, err := client.Get("http://localhost:3001")
        if err != nil {
            w.WriteHeader(http.StatusInternalServerError)
            w.Write([]byte(err.Error()))
            return
        }
        body, err := io.ReadAll(resp.Body)
        if err != nil {
            w.WriteHeader(http.StatusInternalServerError)
            w.Write([]byte(err.Error()))
            return
        }
        defer resp.Body.Close()
        var data response
        err = json.Unmarshal(body, &data)
        if err != nil {
            w.WriteHeader(http.StatusInternalServerError)
            w.Write([]byte(err.Error()))
            return
        }
        w.Header().Set("Content-Type", "application/json")
        w.Write([]byte(`{"messageA": "hello from service A","messageB": "` + data.Message + `"}`))
    })
    http.ListenAndServe(":3000", r)
}

func newRetryPolicy(logger *slog.Logger) retrypolicy.RetryPolicy[*http.Response] {
    return retrypolicy.Builder[*http.Response]().
        HandleIf(func(response *http.Response, _ error) bool {
            return response != nil && response.StatusCode == http.StatusServiceUnavailable
        }).
        WithBackoff(time.Second, 10*time.Second).
        OnRetryScheduled(func(e failsafe.ExecutionScheduledEvent[*http.Response]) {
            logger.Info(fmt.Sprintf("Retry %d after delay of %d", e.Attempts(), e.Delay))
        }).Build()
}

Dengan cara ini, jika serviceB mengembalikan status StatusServiceUnavailable (kod 503), sambungan akan dicuba sekali lagi pada selang progresif, terima kasih kepada konfigurasi fungsi WithBackoff. Output serviceA, apabila diakses melalui curl, haruslah sesuatu yang serupa dengan:

go run main.go
{"time":"2024-08-20T08:43:38.297621-03:00","level":"INFO","msg":"200: OK","request":{"time":"2024-08-20T08:43:38.283715-03:00","method":"GET","host":"localhost:3000","path":"/","query":"","params":{},"route":"/","ip":"[::1]:63542","referer":"","length":0},"response":{"time":"2024-08-20T08:43:38.297556-03:00","latency":13840708,"status":200,"length":71},"id":""}
{"time":"2024-08-20T08:43:39.946562-03:00","level":"INFO","msg":"200: OK","request":{"time":"2024-08-20T08:43:39.943394-03:00","method":"GET","host":"localhost:3000","path":"/","query":"","params":{},"route":"/","ip":"[::1]:63544","referer":"","length":0},"response":{"time":"2024-08-20T08:43:39.946545-03:00","latency":3151000,"status":200,"length":71},"id":""}
{"time":"2024-08-20T08:43:40.845862-03:00","level":"INFO","msg":"Retry 1 after delay of 1000000000"}
{"time":"2024-08-20T08:43:41.85287-03:00","level":"INFO","msg":"Retry 2 after delay of 2000000000"}
{"time":"2024-08-20T08:43:43.860694-03:00","level":"INFO","msg":"200: OK","request":{"time":"2024-08-20T08:43:40.841468-03:00","method":"GET","host":"localhost:3000","path":"/","query":"","params":{},"route":"/","ip":"[::1]:63545","referer":"","length":0},"response":{"time":"2024-08-20T08:43:43.860651-03:00","latency":3019287458,"status":200,"length":71},"id":""}

Dalam contoh ini, adalah mungkin untuk melihat bahawa ralat berlaku semasa mengakses perkhidmatanB dan lib melaksanakan sambungan sekali lagi sehingga ia berjaya. Jika sambungan terus memberikan ralat, pelanggan akan menerima mesej ralat ”http://localhost:3001": percubaan semula melebihi.

Mari kita mendalami daya tahan dengan menambahkan pemutus litar pada projek kami.

Pemutus litar

Konsep pemutus litar ialah dasar yang lebih maju yang memberikan kawalan yang lebih besar ke atas akses kepada perkhidmatan. Pemutus litar corak berfungsi dalam tiga keadaan: tertutup (tiada ralat), buka (dengan ralat, gangguan penghantaran) dan separa terbuka (menghantar bilangan permintaan terhad kepada perkhidmatan yang mengalami kesukaran untuk menguji pemulihannya).

Untuk menggunakan dasar ini, saya membuat versi baharu perkhidmatanB supaya ia boleh menjana lebih banyak senario ralat dan kelewatan:

package main

import (
    "math/rand"
    "net/http"
    "strconv"
    "time"

    "github.com/go-chi/chi/v5"
    "github.com/go-chi/chi/v5/middleware"
)

func main() {
    r := chi.NewRouter()
    r.Use(middleware.Logger)
    r.Get("/", func(w http.ResponseWriter, r *http.Request) {
        retryAfterDelay := 1 * time.Second
        if fail() {
            w.Header().Add("Retry-After", strconv.Itoa(int(retryAfterDelay.Seconds())))
            w.WriteHeader(http.StatusServiceUnavailable)
            return
        }
        if sleep() {
            time.Sleep(1 * time.Second)
        }
        w.Header().Set("Content-Type", "application/json")
        w.Write([]byte(`{"message": "hello from service B"}`))
    })
    http.ListenAndServe(":3001", r)
}

func fail() bool {
    if flipint := rand.Intn(2); flipint == 0 {
        return true
    }
    return false
}

func sleep() bool {
    if flipint := rand.Intn(2); flipint == 0 {
        return true
    }
    return false
}

Dan kod perkhidmatanA:

package main

import (
    "encoding/json"
    "fmt"
    "io"
    "log/slog"
    "net/http"
    "os"
    "time"

    "github.com/failsafe-go/failsafe-go/circuitbreaker"
    "github.com/failsafe-go/failsafe-go/failsafehttp"
    "github.com/go-chi/chi/v5"
    slogchi "github.com/samber/slog-chi"
)

func main() {
    logger := slog.New(slog.NewJSONHandler(os.Stdout, nil))
    r := chi.NewRouter()
    r.Use(slogchi.New(logger))
    r.Get("/", func(w http.ResponseWriter, r *http.Request) {
        type response struct {
            Message string `json:"message"`
        }
        // Create a CircuitBreaker that handles 503 responses and uses a half-open delay based on the Retry-After header
        circuitBreaker := newCircuitBreaker(logger)

        // Use the RetryPolicy with a failsafe RoundTripper
        roundTripper := failsafehttp.NewRoundTripper(nil, circuitBreaker)
        client := &http.Client{Transport: roundTripper}

        sendGet := func() (*http.Response, error) {
            resp, err := client.Get("http://localhost:3001")
            return resp, err
        }
        maxRetries := 3
        resp, err := sendGet()
        for i := 0; i < maxRetries; i++ {
            if err == nil && resp != nil && resp.StatusCode != http.StatusServiceUnavailable && resp.StatusCode != http.StatusTooManyRequests {
                break
            }
            time.Sleep(circuitBreaker.RemainingDelay()) // Wait for circuit breaker's delay, provided by the Retry-After header
            resp, err = sendGet()
        }
        if err != nil {
            w.WriteHeader(http.StatusInternalServerError)
            w.Write([]byte(err.Error()))
            return
        }
        body, err := io.ReadAll(resp.Body)
        if err != nil {
            w.WriteHeader(http.StatusInternalServerError)
            w.Write([]byte(err.Error()))
            return
        }
        defer resp.Body.Close()
        var data response
        err = json.Unmarshal(body, &data)
        if err != nil {
            w.WriteHeader(http.StatusInternalServerError)
            w.Write([]byte(err.Error()))
            return
        }
        w.Header().Set("Content-Type", "application/json")
        w.Write([]byte(`{"messageA": "hello from service A","messageB": "` + data.Message + `"}`))
    })
    http.ListenAndServe(":3000", r)
}

func newCircuitBreaker(logger *slog.Logger) circuitbreaker.CircuitBreaker[*http.Response] {
    return circuitbreaker.Builder[*http.Response]().
        HandleIf(func(response *http.Response, err error) bool {
            return response != nil && response.StatusCode == http.StatusServiceUnavailable
        }).
        WithDelayFunc(failsafehttp.DelayFunc).
        OnStateChanged(func(event circuitbreaker.StateChangedEvent) {
            logger.Info(fmt.Sprintf("circuit breaker state changed from %s to %s", event.OldState.String(), event.NewState.String()))
        }).
        Build()
}

Seperti yang dapat kita lihat dalam output perkhidmatanA, pemutus litar berfungsi:

❯ go run main.go
{"time":"2024-08-20T08:51:37.770611-03:00","level":"INFO","msg":"circuit breaker state changed from closed to open"}
{"time":"2024-08-20T08:51:38.771682-03:00","level":"INFO","msg":"circuit breaker state changed from open to half-open"}
{"time":"2024-08-20T08:51:38.776743-03:00","level":"INFO","msg":"circuit breaker state changed from half-open to open"}
{"time":"2024-08-20T08:51:39.777821-03:00","level":"INFO","msg":"circuit breaker state changed from open to half-open"}
{"time":"2024-08-20T08:51:39.784897-03:00","level":"INFO","msg":"circuit breaker state changed from half-open to open"}
{"time":"2024-08-20T08:51:40.786209-03:00","level":"INFO","msg":"circuit breaker state changed from open to half-open"}
{"time":"2024-08-20T08:51:40.792457-03:00","level":"INFO","msg":"circuit breaker state changed from half-open to closed"}
{"time":"2024-08-20T08:51:40.792733-03:00","level":"INFO","msg":"200: OK","request":{"time":"2024-08-20T08:51:37.756947-03:00","method":"GET","host":"localhost:3000","path":"/","query":"","params":{},"route":"/","ip":"[::1]:63699","referer":"","length":0},"response":{"time":"2024-08-20T08:51:40.792709-03:00","latency":3036065875,"status":200,"length":71},"id":""}

Dasar ini membenarkan kawalan yang lebih besar ke atas ralat, membolehkan serviceB pulih jika ia mengalami masalah.

Tetapi apa yang anda lakukan apabila serviceB tidak lagi boleh kembali, atas sebab apa pun? Dalam kes ini, kita boleh menggunakan sandaran.

Fallback

Idea dasar ini adalah untuk mempunyai alternatif jika perkhidmatan yang dikehendaki mempunyai masalah yang lebih teruk dan mengambil masa yang lama untuk dikembalikan. Untuk melakukan ini, kami akan menukar kod serviceA:

package main

import (
    "bytes"
    "encoding/json"
    "io"
    "log/slog"
    "net/http"
    "os"

    "github.com/failsafe-go/failsafe-go"
    "github.com/failsafe-go/failsafe-go/failsafehttp"
    "github.com/failsafe-go/failsafe-go/fallback"
    "github.com/go-chi/chi/v5"
    slogchi "github.com/samber/slog-chi"
)

func main() {
    logger := slog.New(slog.NewJSONHandler(os.Stdout, nil))
    r := chi.NewRouter()
    r.Use(slogchi.New(logger))
    r.Get("/", func(w http.ResponseWriter, r *http.Request) {
        fallback := newFallback(logger)

        roundTripper := failsafehttp.NewRoundTripper(nil, fallback)
        client := &http.Client{Transport: roundTripper}

        resp, err := client.Get("http://localhost:3001")
        if err != nil {
            w.WriteHeader(http.StatusInternalServerError)
            w.Write([]byte(err.Error()))
            return
        }
        body, err := io.ReadAll(resp.Body)
        if err != nil {
            w.WriteHeader(http.StatusInternalServerError)
            w.Write([]byte(err.Error()))
            return
        }
        defer resp.Body.Close()
        type response struct {
            Message string `json:"message"`
        }
        var data response
        err = json.Unmarshal(body, &data)
        if err != nil {
            w.WriteHeader(http.StatusInternalServerError)
            w.Write([]byte(err.Error()))
            return
        }
        w.Header().Set("Content-Type", "application/json")
        w.Write([]byte(`{"messageA": "hello from service A","messageB": "` + data.Message + `"}`))
    })
    http.ListenAndServe(":3000", r)
}

func newFallback(logger *slog.Logger) fallback.Fallback[*http.Response] {
    resp := &http.Response{
        StatusCode: http.StatusOK,
        Header:     map[string][]string{"Content-Type": {"application/json"}},
        Body:       io.NopCloser(bytes.NewBufferString(`{"message": "error accessing service B"}`)),
    }
    return fallback.BuilderWithResult[*http.Response](resp).
        HandleIf(func(response *http.Response, err error) bool {
            return response != nil && response.StatusCode == http.StatusServiceUnavailable
        }).
        OnFallbackExecuted(func(e failsafe.ExecutionDoneEvent[*http.Response]) {
            logger.Info("Fallback executed result")
        }).
        Build()
}

Dalam fungsi newFallback, kita dapat melihat penciptaan satu http.Response yang akan digunakan oleh lib jika pengguna serviceB tidak bertindak balas.

Ciri ini membolehkan kami bertindak balas kepada pelanggan sementara pasukan yang bertanggungjawab untuk perkhidmatanB mempunyai masa untuk menyediakan perkhidmatan dan berjalan semula.

Keluaran perkhidmatanA adalah serupa dengan ini:

❯ go run main.go
{"time":"2024-08-20T08:55:27.326475-03:00","level":"INFO","msg":"200: OK","request":{"time":"2024-08-20T08:55:27.31306-03:00","method":"GET","host":"localhost:3000","path":"/","query":"","params":{},"route":"/","ip":"[::1]:63772","referer":"","length":0},"response":{"time":"2024-08-20T08:55:27.326402-03:00","latency":13343208,"status":200,"length":71},"id":""}
{"time":"2024-08-20T08:55:31.756765-03:00","level":"INFO","msg":"200: OK","request":{"time":"2024-08-20T08:55:31.754348-03:00","method":"GET","host":"localhost:3000","path":"/","query":"","params":{},"route":"/","ip":"[::1]:63774","referer":"","length":0},"response":{"time":"2024-08-20T08:55:31.756753-03:00","latency":2404750,"status":200,"length":71},"id":""}
{"time":"2024-08-20T08:55:34.091845-03:00","level":"INFO","msg":"200: OK","request":{"time":"2024-08-20T08:55:33.086273-03:00","method":"GET","host":"localhost:3000","path":"/","query":"","params":{},"route":"/","ip":"[::1]:63775","referer":"","length":0},"response":{"time":"2024-08-20T08:55:34.091812-03:00","latency":1005580625,"status":200,"length":71},"id":""}
{"time":"2024-08-20T08:55:37.386512-03:00","level":"INFO","msg":"Fallback executed result"}
{"time":"2024-08-20T08:55:37.386553-03:00","level":"INFO","msg":"200: OK","request":{"time":"2024-08-20T08:55:37.38415-03:00","method":"GET","host":"localhost:3000","path":"/","query":"","params":{},"route":"/","ip":"[::1]:63777","referer":"","length":0},"response":{"time":"2024-08-20T08:55:37.386544-03:00","latency":2393916,"status":200,"length":76},"id":""}

In the next step, we will combine the concepts we've seen to create a more resilient application.

Policy composition

To do this, we need to change the code of serviceA so that it makes use of the policies we have seen so far:

package main

import (
    "bytes"
    "encoding/json"
    "fmt"
    "io"
    "log/slog"
    "net/http"
    "os"
    "time"

    "github.com/failsafe-go/failsafe-go"
    "github.com/failsafe-go/failsafe-go/circuitbreaker"
    "github.com/failsafe-go/failsafe-go/failsafehttp"
    "github.com/failsafe-go/failsafe-go/fallback"
    "github.com/failsafe-go/failsafe-go/retrypolicy"
    "github.com/failsafe-go/failsafe-go/timeout"
    "github.com/go-chi/chi/v5"
    slogchi "github.com/samber/slog-chi"
)

func main() {
    logger := slog.New(slog.NewJSONHandler(os.Stdout, nil))
    r := chi.NewRouter()
    r.Use(slogchi.New(logger))
    r.Get("/", func(w http.ResponseWriter, r *http.Request) {
        type response struct {
            Message string `json:"message"`
        }
        retryPolicy := newRetryPolicy(logger)
        fallback := newFallback(logger)
        circuitBreaker := newCircuitBreaker(logger)
        timeout := newTimeout(logger)

        roundTripper := failsafehttp.NewRoundTripper(nil, fallback, retryPolicy, circuitBreaker, timeout)
        client := &http.Client{Transport: roundTripper}

        sendGet := func() (*http.Response, error) {
            resp, err := client.Get("http://localhost:3001")
            return resp, err
        }
        maxRetries := 3
        resp, err := sendGet()
        for i := 0; i < maxRetries; i++ {
            if err == nil && resp != nil && resp.StatusCode != http.StatusServiceUnavailable && resp.StatusCode != http.StatusTooManyRequests {
                break
            }
            time.Sleep(circuitBreaker.RemainingDelay()) // Wait for circuit breaker's delay, provided by the Retry-After header
            resp, err = sendGet()
        }
        if err != nil {
            w.WriteHeader(http.StatusInternalServerError)
            w.Write([]byte(err.Error()))
            return
        }
        body, err := io.ReadAll(resp.Body)
        if err != nil {
            w.WriteHeader(http.StatusInternalServerError)
            w.Write([]byte(err.Error()))
            return
        }
        defer resp.Body.Close()
        var data response
        err = json.Unmarshal(body, &data)
        if err != nil {
            w.WriteHeader(http.StatusInternalServerError)
            w.Write([]byte(err.Error()))
            return
        }
        w.Header().Set("Content-Type", "application/json")
        w.Write([]byte(`{"messageA": "hello from service A","messageB": "` + data.Message + `"}`))
    })
    http.ListenAndServe(":3000", r)
}

func newTimeout(logger *slog.Logger) timeout.Timeout[*http.Response] {
    return timeout.Builder[*http.Response](10 * time.Second).
        OnTimeoutExceeded(func(e failsafe.ExecutionDoneEvent[*http.Response]) {
            logger.Info("Connection timed out")
        }).Build()
}

func newFallback(logger *slog.Logger) fallback.Fallback[*http.Response] {
    resp := &http.Response{
        StatusCode: http.StatusOK,
        Header:     map[string][]string{"Content-Type": {"application/json"}},
        Body:       io.NopCloser(bytes.NewBufferString(`{"message": "error accessing service B"}`)),
    }
    return fallback.BuilderWithResult[*http.Response](resp).
        HandleIf(func(response *http.Response, err error) bool {
            return response != nil && response.StatusCode == http.StatusServiceUnavailable
        }).
        OnFallbackExecuted(func(e failsafe.ExecutionDoneEvent[*http.Response]) {
            logger.Info("Fallback executed result")
        }).
        Build()
}

func newRetryPolicy(logger *slog.Logger) retrypolicy.RetryPolicy[*http.Response] {
    return retrypolicy.Builder[*http.Response]().
        HandleIf(func(response *http.Response, _ error) bool {
            return response != nil && response.StatusCode == http.StatusServiceUnavailable
        }).
        WithBackoff(time.Second, 10*time.Second).
        OnRetryScheduled(func(e failsafe.ExecutionScheduledEvent[*http.Response]) {
            logger.Info(fmt.Sprintf("Retry %d after delay of %d", e.Attempts(), e.Delay))
        }).Build()
}

func newCircuitBreaker(logger *slog.Logger) circuitbreaker.CircuitBreaker[*http.Response] {
    return circuitbreaker.Builder[*http.Response]().
        HandleIf(func(response *http.Response, err error) bool {
            return response != nil && response.StatusCode == http.StatusServiceUnavailable
        }).
        WithDelayFunc(failsafehttp.DelayFunc).
        OnStateChanged(func(event circuitbreaker.StateChangedEvent) {
            logger.Info(fmt.Sprintf("circuit breaker state changed from %s to %s", event.OldState.String(), event.NewState.String()))
        }).
        Build()
}

In the code:

roundTripper := failsafehttp.NewRoundTripper(nil, fallback, retryPolicy, circuitBreaker, timeout)

It is possible to view the use of all defined policies. The lib will execute it in the "rightmost" order, that is:

timeout -> circuitBreaker -> retryPolicy -> fallback

We can see the execution of the policies by observing the serviceA output:

go run main.go
{"time":"2024-08-19T10:15:29.226553-03:00","level":"INFO","msg":"circuit breaker state changed from closed to open"}
{"time":"2024-08-19T10:15:29.226841-03:00","level":"INFO","msg":"Retry 1 after delay of 1000000000"}
{"time":"2024-08-19T10:15:30.227941-03:00","level":"INFO","msg":"circuit breaker state changed from open to half-open"}
{"time":"2024-08-19T10:15:30.234182-03:00","level":"INFO","msg":"circuit breaker state changed from half-open to open"}
{"time":"2024-08-19T10:15:30.234258-03:00","level":"INFO","msg":"Retry 2 after delay of 2000000000"}
{"time":"2024-08-19T10:15:32.235282-03:00","level":"INFO","msg":"circuit breaker state changed from open to half-open"}
{"time":"2024-08-19T10:15:42.23622-03:00","level":"INFO","msg":"Connection timed out"}
{"time":"2024-08-19T10:15:42.237942-03:00","level":"INFO","msg":"circuit breaker state changed from half-open to closed"}
{"time":"2024-08-19T10:15:42.238043-03:00","level":"ERROR","msg":"500: Internal Server Error","request":{"time":"2024-08-19T10:15:29.215709-03:00","method":"GET","host":"localhost:3000","path":"/","query":"","params":{},"route":"/","ip":"[::1]:52527","referer":"","length":0},"response":{"time":"2024-08-19T10:15:42.238008-03:00","latency":13022704750,"status":500,"length":45},"id":""}
{"time":"2024-08-19T10:15:56.53476-03:00","level":"INFO","msg":"circuit breaker state changed from closed to open"}
{"time":"2024-08-19T10:15:56.534803-03:00","level":"INFO","msg":"Retry 1 after delay of 1000000000"}
{"time":"2024-08-19T10:15:57.535108-03:00","level":"INFO","msg":"circuit breaker state changed from open to half-open"}
{"time":"2024-08-19T10:15:57.53889-03:00","level":"INFO","msg":"circuit breaker state changed from half-open to open"}
{"time":"2024-08-19T10:15:57.538911-03:00","level":"INFO","msg":"Retry 2 after delay of 2000000000"}
{"time":"2024-08-19T10:15:59.539948-03:00","level":"INFO","msg":"circuit breaker state changed from open to half-open"}
{"time":"2024-08-19T10:15:59.544425-03:00","level":"INFO","msg":"circuit breaker state changed from half-open to open"}
{"time":"2024-08-19T10:15:59.544575-03:00","level":"ERROR","msg":"500: Internal Server Error","request":{"time":"2024-08-19T10:15:56.5263-03:00","method":"GET","host":"localhost:3000","path":"/","query":"","params":{},"route":"/","ip":"[::1]:52542","referer":"","length":0},"response":{"time":"2024-08-19T10:15:59.544557-03:00","latency":3018352000,"status":500,"length":245},"id":""}
{"time":"2024-08-19T10:16:11.044207-03:00","level":"INFO","msg":"Connection timed out"}
{"time":"2024-08-19T10:16:11.046026-03:00","level":"ERROR","msg":"500: Internal Server Error","request":{"time":"2024-08-19T10:16:01.043317-03:00","method":"GET","host":"localhost:3000","path":"/","query":"","params":{},"route":"/","ip":"[::1]:52544","referer":"","length":0},"response":{"time":"2024-08-19T10:16:11.045601-03:00","latency":10002596334,"status":500,"length":45},"id":""}

Conclusion

One of the advantages of microservices architecture is that we can break a complex domain into smaller, specialized services that communicate with each other to complete the necessary logic. Ensuring that this communication is resilient and will continue to work even in the face of failures and unforeseen events is fundamental. Using libraries such as failsafe-go makes this process easier.

You can find the codes presented in this post on my Github.

Originally published at https://eltonminetto.dev on August 24, 2024

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