I tried to setup telegraf with docker with the tail plugin enabled.
My telegraf.conf looks like this:

[agent]
  interval = "10s"
  round_interval = true
  metric_batch_size = 1000
  metric_buffer_limit = 10000

[[outputs.influxdb_v2]]
  urls = ["http://influxdb:8086"]
  token = "TOKEN"
  organization = "ORG"
  bucket = "BUCKET"

[[inputs.tail]]
  files = ["/var/log/syslog-ng/192.168.10.1.log"]
  from_beginning = true
  data_format = "grok"
  grok_patterns = ['%{TIMESTAMP_ISO8601:timestamp} %{IPV4:host} %{DATA:topics} %{GREEDYDATA:message}']

  [inputs.tail.tags]
    logsource = "logsource"

my docker-compose.yml

  telegraf:
    image: telegraf:1.29-alpine
    container_name: telegraf
    command: -debug
    volumes:
      - ./data/telegraf/config/telegraf.conf:/etc/telegraf/telegraf.conf
      - ./data/syslog-ng/log:/var/log/syslog-ng

docker logs -f telegraf output:

2024-07-23T09:51:14Z I! Loading config: /etc/telegraf/telegraf.conf
2024-07-23T09:51:14Z I! Starting Telegraf 1.29.5 brought to you by InfluxData the makers of InfluxDB
2024-07-23T09:51:14Z I! Available plugins: 241 inputs, 9 aggregators, 30 processors, 24 parsers, 60 outputs, 6 secret-stores
2024-07-23T09:51:14Z I! Loaded inputs: tail
2024-07-23T09:51:14Z I! Loaded aggregators:
2024-07-23T09:51:14Z I! Loaded processors:
2024-07-23T09:51:14Z I! Loaded secretstores:
2024-07-23T09:51:14Z I! Loaded outputs: influxdb_v2
2024-07-23T09:51:14Z I! Tags enabled: host=d6eaa952a62d
2024-07-23T09:51:14Z I! [agent] Config: Interval:10s, Quiet:false, Hostname:"d6eaa952a62d", Flush Interval:10s
2024-07-23T09:51:14Z D! [agent] Initializing plugins
2024-07-23T09:51:14Z D! [agent] Connecting outputs
2024-07-23T09:51:14Z D! [agent] Attempting connection to [outputs.influxdb_v2]
2024-07-23T09:51:14Z D! [agent] Successfully connected to outputs.influxdb_v2
2024-07-23T09:51:14Z D! [agent] Starting service inputs
2024-07-23T09:51:24Z D! [outputs.influxdb_v2] Buffer fullness: 0 / 10000 metrics
2024-07-23T09:51:34Z D! [outputs.influxdb_v2] Buffer fullness: 0 / 10000 metrics
2024-07-23T09:51:44Z D! [outputs.influxdb_v2] Buffer fullness: 0 / 10000 metrics
2024-07-23T09:51:54Z D! [outputs.influxdb_v2] Buffer fullness: 0 / 10000 metrics
2024-07-23T09:52:04Z D! [outputs.influxdb_v2] Buffer fullness: 0 / 10000 metrics

and no metrics are pushed in the bucket on influxdb.

When I enter the container docker exec -it telegraf sh and execute telegraf -debug it reads the conf complete and started the tail plugin:

2024-07-23T09:54:42Z I! Loading config: /etc/telegraf/telegraf.conf
2024-07-23T09:54:42Z I! Starting Telegraf 1.29.5 brought to you by InfluxData the makers of InfluxDB
2024-07-23T09:54:42Z I! Available plugins: 241 inputs, 9 aggregators, 30 processors, 24 parsers, 60 outputs, 6 secret-stores
2024-07-23T09:54:42Z I! Loaded inputs: tail
2024-07-23T09:54:42Z I! Loaded aggregators:
2024-07-23T09:54:42Z I! Loaded processors:
2024-07-23T09:54:42Z I! Loaded secretstores:
2024-07-23T09:54:42Z I! Loaded outputs: influxdb_v2
2024-07-23T09:54:42Z I! Tags enabled: host=d6eaa952a62d
2024-07-23T09:54:42Z I! [agent] Config: Interval:10s, Quiet:false, Hostname:"d6eaa952a62d", Flush Interval:10s
2024-07-23T09:54:42Z D! [agent] Initializing plugins
2024-07-23T09:54:42Z D! [agent] Connecting outputs
2024-07-23T09:54:42Z D! [agent] Attempting connection to [outputs.influxdb_v2]
2024-07-23T09:54:42Z D! [agent] Successfully connected to outputs.influxdb_v2
2024-07-23T09:54:42Z D! [agent] Starting service inputs
2024-07-23T09:54:42Z D! [inputs.tail] Tail added for "/var/log/syslog-ng/192.168.10.1.log"
2024-07-23T09:54:42Z D! [outputs.influxdb_v2] Wrote batch of 1000 metrics in 82.347552ms
2024-07-23T09:54:42Z D! [outputs.influxdb_v2] Buffer fullness: 0 / 10000 metrics
2024-07-23T09:54:42Z D! [outputs.influxdb_v2] Wrote batch of 1000 metrics in 15.768439ms
2024-07-23T09:54:42Z D! [outputs.influxdb_v2] Buffer fullness: 0 / 10000 metrics
2024-07-23T09:54:42Z D! [outputs.influxdb_v2] Wrote batch of 1000 metrics in 30.661502ms
2024-07-23T09:54:42Z D! [outputs.influxdb_v2] Buffer fullness: 0 / 10000 metrics

When started with docker compose up -d the following entry is missing:
[inputs.tail] Tail added for "/var/log/syslog-ng/192.168.10.1.log"

Anyone know my mistake?