Container Support and Troubleshooting

Overview

The NGINX Agent repository includes Dockerfiles that can be used to build custom container images. Images are created with an NGINX Open Source or NGINX Plus instance and are available for various operating systems.

See the Technical Specifications for a list of supported operationg systems.

NGINX Agent running in a container has some limitations that need to be considered, and are listed below.

Supported cgroups

To collect metrics about the Docker container that the NGINX Agent is running in, NGINX Agent uses the available cgroup files to calculate metrics like CPU and memory usage.

NGINX Agent supports both versions of cgroups.

Metrics

Unsupported Metrics

The following system metrics are not supported when running NGINX Agent in a Docker container. NGINX Agent returns no values for these metrics:

system.cpu.idle
system.cpu.iowait
system.cpu.stolen
system.mem.buffered
system.load.1
system.load.5
system.load.15
system.disk.total
system.disk.used
system.disk.free
system.disk.in_use
system.io.kbs_r
system.io.kbs_w
system.io.wait_r
system.io.wait_w
system.io.iops_r
system.io.iops_w

Memory Metrics

If no memory limit is set when starting the Docker container, then the memory limit that’s shown in the metrics for the container will be the total memory of the Docker host system.

Swap Memory Metrics

If a warning message similar to the following example is seen in the NGINX Agent logs, the swap memory limit for the Docker container is greater than the swap memory for the Docker host system:

Swap memory limit specified for the container, ... is greater than the host system swap memory ...

The system.swap.total metric for the container matches the total swap memory for the Docker host system instead of the swap memory limit specified when starting the Docker container.

If a warning message similar to the following example is seen in the NGINX Agent logs, the Docker host system does not have cgroup swap limit capabilities enabled. To enable these capabilities, follow the steps below.

Unable to collect Swap metrics because the file ... was not found

Enable cgroup swap limit capabilities

Run the following command to see if the cgroup swap limit capabilities are enabled:

$ docker info | grep swap
WARNING: No swap limit support

To enable cgroup swap limit capabilities, refer to this Docker guide: Docker - Linux post-installation steps.