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📓 Lab 2.2: Running Containers as Instances

Let’s run some instances as examples. You may notice the instance keyword is new, and you might be curious about the meaning of docker:// in this context. When used here, it automatically pulls an image from the Docker Hub and converts into a SIF image. Following this process, the name of the instance is specified.

$ sudo singularity instance start --writable-tmpfs –net \
       --network-args “portmap=8080:80/tcp” \
       docker://nginx:1.23.4-alpine webserver
INFO:    Converting OCI blobs to SIF format
INFO:    Starting build...
Getting image source signatures
Copying blob f56be85fc22e done  
Copying blob 1f21f983520d done  
Copying blob 59b9d2200e63 done  
Copying blob 3e1e579c95fe done  
Copying blob 547a97583f72 done  
Copying blob 2ce963c369bc done  
Copying blob c23b4f8cf279 done  
Copying config 3f8c932fa7 done  
Writing manifest to image destination
Storing signatures
2023/03/30 00:57:11  info unpack layer: sha256:f56be85fc223d[...]d7c4e5add29d7f6
2023/03/30 00:57:11  info unpack layer: sha256:2ce963c369b51[...]dfcc1e286051b5a
2023/03/30 00:57:11  info unpack layer: sha256:59b9d2200e646[...]244c38ebe8d3bee
2023/03/30 00:57:11  info unpack layer: sha256:3e1e579c95f8c[...]af9dbe6219dc649
2023/03/30 00:57:11  info unpack layer: sha256:547a97583f77d[...]83ffa18e0c40fd8
2023/03/30 00:57:11  info unpack layer: sha256:1f21f98352062[...]dd79878071181b5
2023/03/30 00:57:11  info unpack layer: sha256:c23b4f8cf27eb[...]ac215ab5b529aa8
INFO:    Creating SIF file...
INFO:    instance started successfully

The above command creates an instance and starts the official NGINX image running in the background. The instance needs writing to disk, so we’ve set the --writable-tmpfs flag to allocate space in memory.

The --net flag is required when using the --network-args option, as in this example, where we are mapping the port 80 inside the container to port 8080 on the host or workstation.

We are using sudo because real administrative privileges are needed to
manipulate internal system firewall (iptables) and network setup (create a
bridged network interface).

Next, we can list our instances running in the host:

$ sudo singularity instance list
INSTANCE NAME    PID       IP           IMAGE
web              232106    10.22.0.6    /root/.singularity/cache/oci...

Next, let's start the NGINX web server inside the container:
$ sudo singularity exec instance://webserver nginx
023/03/30 01:06:50 [notice] 14#14: using the "epoll" event method
2023/03/30 01:06:50 [notice] 14#14: nginx/1.23.4
2023/03/30 01:06:50 [notice] 14#14: built by gcc 12.2.1 20220924 (Alpine 12.2.1) 
2023/03/30 01:06:50 [notice] 14#14: OS: Linux 6.2.7-200.fc37.x86_64
2023/03/30 01:06:50 [notice] 14#14: getrlimit(RLIMIT_NOFILE): 524288:524288
2023/03/30 01:06:50 [notice] 20#20: start worker processes
2023/03/30 01:06:50 [notice] 20#20: start worker process 21
2023/03/30 01:06:50 [notice] 20#20: start worker process 22
2023/03/30 01:06:50 [notice] 20#20: start worker process 23
2023/03/30 01:06:50 [notice] 20#20: start worker process 24
2023/03/30 01:06:50 [notice] 20#20: start worker process 25
2023/03/30 01:06:50 [notice] 20#20: start worker process 26
2023/03/30 01:06:50 [notice] 20#20: start worker process 27
2023/03/30 01:06:50 [notice] 20#20: start worker process 28
2023/03/30 01:06:50 [notice] 20#20: start worker process 29
2023/03/30 01:06:50 [notice] 20#20: start worker process 30
2023/03/30 01:06:50 [notice] 20#20: start worker process 31
2023/03/30 01:06:50 [notice] 20#20: start worker process 32

Then we can open our browser and load http://localhost:8080 to verify we are running a local webserver.

$ curl http://localhost:8080
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
html { color-scheme: light dark; }
body { width: 35em; margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif; }
10.22.0.1 - - [30/Mar/2023:01:08:27 -0600] "GET / HTTP/1.1" 200 615 "-" "curl/7.85.0" "-"
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>

Besides running a command against an instance and listing the current instances in our host, we can perform other operations. For example, services typically run in the background and write to the standard output. SingularityCE collects standard output and error data into log files for easy access and review.

To view the location of these log files, use the --log option like so:

$ sudo singularity instance list --logs
INSTANCE NAME    PID       LOGS
web              263932    /root/.singularity/web.err
                           /root/.singularity/web.out

Our last operation against an instance in this tutorial is to actually terminate and stop it.

$ sudo singularity instance stop webserver
INFO:    Stopping web instance of /root/.singularity/...a5538d0158f (PID=232106)