interlink-apptainer-plugin

An interLink sidecar plugin that runs container workloads directly via Apptainer — without a batch-scheduler layer.

Compared to the interlink-slurm-plugin, this plugin skips SLURM batch-job submission (sbatch/squeue/scancel) and instead executes job.sh directly as an OS subprocess. This is designed for the use-case where the plugin process is already running inside a job (one job ↔ one virtual node), so no additional scheduling step is needed.

How it works

1. The interlink Virtual Kubelet sends a Create request to the plugin.
2. The plugin generates job.sh — a shell script that runs each container image via apptainer run / apptainer exec (identical logic to the SLURM plugin).
3. job.sh is executed directly as a child process (no sbatch). The process PID is used as the "job ID".
4. Container status is determined by:
   • Checking whether the child process is still alive (kill -0 <pid>).
   • Reading per-container .status files that job.sh writes upon exit.
5. Deleting a pod sends SIGTERM to the entire process group.

Configuration

The plugin reads a YAML configuration file. The default path is /etc/interlink/ApptainerConfig.yaml; override via the APPTAINERCONFIGPATH environment variable or the -ApptainerConfigpath flag.

# Port to listen on (when not using a Unix socket)
SidecarPort: "4000"

# Optional Unix socket path (e.g. "unix:///tmp/apptainer.sock")
# Socket: ""

# Directory where per-pod working data is stored
DataRootFolder: "/tmp/.interlink/"

# Path to the apptainer binary
ApptainerPath: "apptainer"

# Default options passed to every apptainer run/exec call
ApptainerDefaultOptions:
  - "--nv"
  - "--no-eval"
  - "--containall"

# Prefix added to image names that have no URI scheme
# ImagePrefix: "docker://"

# Path to bash used to execute job.sh
BashPath: "/bin/bash"

# Whether to export pod data (ConfigMaps, Secrets) to the working directory
ExportPodData: true

# Verbose / errors-only logging
VerboseLogging: false
ErrorsOnlyLogging: false

# Enable Kubernetes probe support
EnableProbes: false

Environment variable overrides

Variable	Config field
APPTAINERCONFIGPATH	config file path
SIDECARPORT	SidecarPort
APPTAINERPATH	ApptainerPath
TSOCKS	Tsocks
TSOCKSPATH	TsocksPath

Building

go build -o bin/apptainer-plugin ./cmd

Running

APPTAINERCONFIGPATH=/etc/interlink/ApptainerConfig.yaml ./bin/apptainer-plugin

Differences from the SLURM plugin

Feature	SLURM plugin	Apptainer plugin
Job submission	sbatch	Direct exec
Status polling	squeue	kill -0 <pid> + .status files
Job cancellation	scancel	SIGTERM to process group
Cluster info endpoint	sinfo -s	apptainer version
Flavors / SLURM flags	Yes	No
Container runtime	singularity / enroot	apptainer