Scale services using compose command

Hai semuanya di materi kali ini kita akan membahas tentang system scale services dengan docker-compose command. Diantaranya yang akan kita bahas

1. Scale up and down a service
2. What happens in background
3. Execute command specify container

Ok langsung aja kita ke pembahasan yang pertama yaitu

Scale up and down a service

By default docker compose akan membuat semua servicenya dalam 1 instance, now we will create a web service, try to scale this service, and add load blancer.

Berikut adalah default.template.conf file untuk nginx proxy ke backend service

Sekarang coba jalankan dengan perintah docker-compose up -d maka hasilnya seperti berikut:

➜ docker  docker-compose -f .\09-docker-compose\scale\docker-compose.yaml -p scale up -d
Creating network "scale_default" with the default driver
Creating scale_backend_1 ... done
Creating scale_proxy_1   ... done

➜ docker  docker-compose -f .\09-docker-compose\scale\docker-compose.yaml -p scale ps
     Name                    Command               State                Ports
-------------------------------------------------------------------------------------------
scale_backend_1   /docker-entrypoint.sh ngin ...   Up      80/tcp
scale_proxy_1     /docker-entrypoint.sh ngin ...   Up      0.0.0.0:80->80/tcp,:::80->80/tcp

Scale the backend service to 2 with command docker-compose up -d --scale <service-name>=<instance-numbers>:

docker-compose up -d --scale backend=3

Jika dijalankan maka hasilnya seperti berikut:

➜ docker  docker-compose -f .\09-docker-compose\scale\docker-compose.yaml -p scale up -d --scale backend=3
scale_proxy_1 is up-to-date
Creating scale_backend_2 ... done
Creating scale_backend_3 ... done

➜ docker  docker-compose -f .\09-docker-compose\scale\docker-compose.yaml -p scale ps
     Name                    Command               State                Ports
-------------------------------------------------------------------------------------------
scale_backend_1   /docker-entrypoint.sh ngin ...   Up      80/tcp
scale_backend_2   /docker-entrypoint.sh ngin ...   Up      80/tcp
scale_backend_3   /docker-entrypoint.sh ngin ...   Up      80/tcp
scale_proxy_1     /docker-entrypoint.sh ngin ...   Up      0.0.0.0:80->80/tcp,:::80->80/tcp

What happens in background

Scalling service instance pada docker-compose jika kita gambarkan maka seperti berikut:

By default docker akan menambahkan loadbalancer dengan konfigurasi Round Robin

Pada contoh diatas kita melakukan reverse proxy dari service proxy ke service backend yaitu http://backend:80, dengan round-robin load balancing maka jika ada setiap request dari service proxy ke backend maka terminologinya akan seperti berikut:

1. The first request is sent to backend_1.
2. The second request is sent to backend_2.
3. The third request is sent to backend_3.

Sekarang coba akses localhost:80 pada browser kemudian refresh beberapa kali, kemudian access logs pada service backend dengan perintah seperti berikut:

➜ docker  docker-compose -f .\09-docker-compose\scale\docker-compose.yaml -p scale logs --tail 1 -f backend
Attaching to scale_backend_4, scale_backend_3, scale_backend_2
backend_2  | 172.20.0.3 - - [02/Sep/2021:22:10:22 +0000] "GET / HTTP/1.1" 200 3105 "-" "curl/7.78.0" "-"
backend_3  | 172.20.0.3 - - [02/Sep/2021:22:10:12 +0000] "GET / HTTP/1.1" 200 3105 "-" "curl/7.78.0" "-"
backend_4  | 2021/09/02 22:10:48 [notice] 1#1: start worker process 35
backend_2  | 172.20.0.3 - - [02/Sep/2021:22:10:57 +0000] "GET / HTTP/1.1" 200 3105 "-" "curl/7.78.0" "-"
backend_4  | 172.20.0.3 - - [02/Sep/2021:22:10:59 +0000] "GET / HTTP/1.1" 200 3105 "-" "curl/7.78.0" "-"
backend_3  | 172.20.0.3 - - [02/Sep/2021:22:11:06 +0000] "GET / HTTP/1.1" 200 3105 "-" "curl/7.78.0" "-"
backend_4  | 172.20.0.3 - - [02/Sep/2021:22:11:10 +0000] "GET / HTTP/1.1" 200 3105 "-" "curl/7.78.0" "-" 

Execute command specify index of containers

Jika kita mau melakukan execute command dari suatu instance container, kita bisa menggunakan --index pada perintah docker-compose exec sebagai contoh kita akan meng-execute command pada container scale_backend_2 maka gunakan perintah seperti berikut

docker-compose exec --index 2 backend

Jika dijalankan hasilnya seperti berikut:

➜ docker  docker container ls -f name=backend
CONTAINER ID   IMAGE          COMMAND                  CREATED             STATUS             PORTS     NAMES
bcbe6b682276   nginx:alpine   "/docker-entrypoint.…"   14 minutes ago      Up 13 minutes      80/tcp    scale_backend_4
40ab3eb5c0ae   nginx:alpine   "/docker-entrypoint.…"   About an hour ago   Up About an hour   80/tcp    scale_backend_3
9b6a94cdd432   nginx:alpine   "/docker-entrypoint.…"   About an hour ago   Up About an hour   80/tcp    scale_backend_2

➜ docker  docker-compose -f .\09-docker-compose\scale\docker-compose.yaml -p scale exec --index 2 backend hostname
9b6a94cdd432

➜ docker  docker-compose -f .\09-docker-compose\scale\docker-compose.yaml -p scale exec --index 2 backend curl localhost
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