Merge pull request #32 from Roblox/logging

Add support for $(nomad alloc logs) command.

Author: shishir-a412ed

README.md

@@ -138,13 +138,11 @@ Ubuntu (>= 16.04)
 `nomad-driver-containerd` [`v0.1`](https://github.com/Roblox/nomad-driver-containerd/releases/tag/v0.1) is **not** production ready.
 There are some open items which are currently being worked on.
 
-1) **Logging**: Logging is currently not supported i.e `nomad alloc logs` command won't work out-of-the-box for containers launched using `nomad-driver-containerd`. As a workaround, one can use `containerd` command line tool `ctr` to attach to container `stdout/stderr`. Both the issue and workaround is documented [`here`](https://github.com/Roblox/nomad-driver-containerd/issues/30)
+1) **Networking**: Networking is **not in scope** of containerd as described [`here`](https://kubernetes.io/blog/2017/11/containerd-container-runtime-options-kubernetes/). However an external CNI plugin can be used to add networking to the container. We are researching on how to enable networking for our internal use-cases, and would publish (open-source) that work at some point.
 
-2) **Networking**: Networking is **not in scope** of containerd as described [`here`](https://kubernetes.io/blog/2017/11/containerd-container-runtime-options-kubernetes/). However an external CNI plugin can be used to add networking to the container. We are researching on how to enable networking for our internal use-cases, and would publish (open-source) that work at some point.
+2) **Port forwarding**: The ability to map a host port to a container port. This is currently not supported, but could be supported in future.
 
-3) **Port forwarding**: The ability to map a host port to a container port. This is currently not supported, but could be supported in future.
-
-4) **Consul connect**: When a user launches a job in `nomad`, s/he can add a [`service stanza`](https://www.nomadproject.io/docs/job-specification/service) which will instruct `nomad` to register the service with `consul` for service discovery. This is currently not supported.
+3) **Consul connect**: When a user launches a job in `nomad`, s/he can add a [`service stanza`](https://www.nomadproject.io/docs/job-specification/service) which will instruct `nomad` to register the service with `consul` for service discovery. This is currently not supported.
 
 ## License
 

containerd/containerd.go

@@ -19,6 +19,8 @@ package containerd
 
 import (
 	"fmt"
+	"os"
+	"syscall"
 
 	"github.com/containerd/containerd"
 	"github.com/containerd/containerd/cio"
@@ -120,8 +122,24 @@ func (d *Driver) loadContainer(id string) (containerd.Container, error) {
 	return d.client.LoadContainer(d.ctxContainerd, id)
 }
 
-func (d *Driver) createTask(container containerd.Container) (containerd.Task, error) {
-	return container.NewTask(d.ctxContainerd, cio.NewCreator(cio.WithStdio))
+func (d *Driver) createTask(container containerd.Container, stdoutPath, stderrPath string) (containerd.Task, error) {
+	stdout, err := openFIFO(stdoutPath)
+	if err != nil {
+		return nil, err
+	}
+
+	stderr, err := openFIFO(stderrPath)
+	if err != nil {
+		return nil, err
+	}
+
+	return container.NewTask(d.ctxContainerd, cio.NewCreator(cio.WithStreams(nil, stdout, stderr)))
+}
+
+// FIFO's are named pipes in linux.
+// openFIFO() opens the nomad task stdout/stderr pipes and returns the fd.
+func openFIFO(path string) (*os.File, error) {
+	return os.OpenFile(path, os.O_RDWR|syscall.O_NONBLOCK, 0600)
 }
 
 func (d *Driver) getTask(container containerd.Container) (containerd.Task, error) {

containerd/driver.go

@@ -359,7 +359,7 @@ func (d *Driver) StartTask(cfg *drivers.TaskConfig) (*drivers.TaskHandle, *drive
 
 	d.logger.Info(fmt.Sprintf("Successfully created container with name: %s", containerName))
 
-	task, err := d.createTask(container)
+	task, err := d.createTask(container, cfg.StdoutPath, cfg.StderrPath)
 	if err != nil {
 		return nil, nil, fmt.Errorf("Error in creating task: %v", err)
 	}