dockron/main.go

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package main
import (
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"flag"
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"fmt"
"github.com/docker/docker/api/types"
"github.com/docker/docker/client"
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"github.com/robfig/cron/v3"
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"golang.org/x/net/context"
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"log"
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"os"
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"strings"
"time"
)
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var (
// defaultWatchInterval is the duration we should sleep until polling Docker
defaultWatchInterval = (1 * time.Minute)
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// schedLabel is the string label to search for cron expressions
schedLabel = "dockron.schedule"
// version of dockron being run
version = "dev"
)
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// ContainerStartJob represents a scheduled container task
// It contains a reference to a client, the schedule to run on, and the
// ID of that container that should be started
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type ContainerStartJob struct {
Client *client.Client
ContainerID string
Context context.Context
Name string
Schedule string
}
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// Run is executed based on the ContainerStartJob Schedule and starts the
// container
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func (job ContainerStartJob) Run() {
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log.Println("Starting:", job.Name)
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err := job.Client.ContainerStart(job.Context, job.ContainerID, types.ContainerStartOptions{})
if err != nil {
panic(err)
}
}
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// QueryScheduledJobs queries Docker for all containers with a schedule and
// returns a list of ContainerStartJob records to be scheduled
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func QueryScheduledJobs(cli *client.Client) (jobs []ContainerStartJob) {
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log.Println("Scanning containers for new schedules...")
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containers, err := cli.ContainerList(context.Background(), types.ContainerListOptions{All: true})
if err != nil {
panic(err)
}
for _, container := range containers {
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if val, ok := container.Labels[schedLabel]; ok {
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jobName := strings.Join(container.Names, "/")
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jobs = append(jobs, ContainerStartJob{
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Schedule: val,
Client: cli,
ContainerID: container.ID,
Context: context.Background(),
Name: jobName,
})
}
}
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return
}
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// ScheduleJobs accepts a Cron instance and a list of jobs to schedule.
// It then schedules the provided jobs
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func ScheduleJobs(c *cron.Cron, jobs []ContainerStartJob) {
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for _, job := range jobs {
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// TODO: Do something with the entryId returned here
_, err := c.AddJob(job.Schedule, job)
if err == nil {
log.Printf("Scheduled %s (%s) with schedule '%s'\n", job.Name, job.ContainerID[:10], job.Schedule)
} else {
// TODO: Track something for a healthcheck here
log.Printf("Error scheduling %s (%s) with schedule '%s'. %v", job.Name, job.ContainerID[:10], job.Schedule, err)
}
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}
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}
func main() {
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// Get a Docker Client
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cli, err := client.NewEnvClient()
if err != nil {
panic(err)
}
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// Read interval for polling Docker
var watchInterval time.Duration
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flag.DurationVar(&watchInterval, "watch", defaultWatchInterval, "Interval used to poll Docker for changes")
var showVersion = flag.Bool("version", false, "Display the version of dockron and exit")
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flag.Parse()
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// Print version if asked
if *showVersion {
fmt.Println("Dockron version:", version)
os.Exit(0)
}
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// Create a Cron
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c := cron.New()
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// Start the loop
for {
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// HACK: This is risky as it could fall on the same interval as a task and that task would get skipped
// It would be best to manage a ContainerID to Job mapping and then remove entries that are missing
// in the new list and add new entries. However, cron does not support this yet.
// Stop and create a new cron
c.Stop()
c = cron.New()
// Schedule jobs again
jobs := QueryScheduledJobs(cli)
ScheduleJobs(c, jobs)
c.Start()
// Sleep until the next query time
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time.Sleep(watchInterval)
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}
}