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Install Alloy

sudo mkdir -p /etc/apt/keyrings/
wget -q -O- https://apt.grafana.com/gpg.key | gpg --dearmor | sudo tee /etc/apt/keyrings/grafana.gpg > /dev/null
echo "deb [signed-by=/etc/apt/keyrings/grafana.gpg] https://apt.grafana.com stable main" | sudo tee /etc/apt/sources.list.d/grafana.list

sudo apt update
sudo apt install -y alloy

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Config

Edit /etc/alloy/config.alloy: 
local.file_match "api_logs" {
  path_targets = [
    {
      __path__ = "/home/deploy/apps/J-Optic-Backend/logs/api-joptic.log",
      job      = "pm2",
      app      = "joptic",
      host     = "vps",
    },
    {
      __path__ = "/home/deploy/apps/J-Optic-SuperAdmin/logs/api-jsuper-admin.log",
      job      = "pm2",
      app      = "jsuper-admin",
      host     = "vps",
    },
    {
      __path__ = "/var/log/nginx/access.log",
      job = "nginx",
      type = "access",
    },
    {
      __path__ = "/var/log/nginx/error.log",
      job = "nginx",
      type = "error",
    },
  ]
}

loki.source.file "api_logs" {
  targets    = local.file_match.api_logs.targets
  forward_to = [loki.write.default.receiver]
}

loki.write "default" {
  endpoint {
    url = "http://127.0.0.1:4100/loki/api/v1/push"
  }
}
Defines the log files Alloy should watch. Each entry in path_targets is a file path plus labels (job, app, host, type) that get attached to every log line shipped from that file — these labels are what you filter on later in Grafana/Loki queries.
Tails the files matched above and forwards new log lines to the configured receiver.
Pushes the collected logs to Loki’s push API. The endpoint matches the Loki setup running on port 4100 (http://127.0.0.1:4100/loki/api/v1/push).
Add a new block inside path_targets for every new app you deploy — just point __path__ at its PM2 log file and give it a unique app label.

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systemd service

The Alloy package installs a systemd service automatically at /etc/systemd/system/alloy.service. Enable and start it: 
sudo systemctl enable alloy
sudo systemctl start alloy
If you need to check or edit the service definition: 
sudo systemctl cat alloy
Only Alloy needs restarting after editing /etc/alloy/config.alloy — Loki and Grafana don’t need to be touched for log-source config changes.

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Restart Alloy after config changes

sudo systemctl restart alloy
sudo systemctl status alloy --no-pager

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Verify it’s shipping logs

sudo journalctl -u alloy -f