Using empty groups in the inventory

[bbbbbrie]

🌊 Heya! I noticed that spot seems to handle things gracefully when there are empty groups in the inventory. For how I am using spot with my team, I would like to know:

• Was spot designed specifically to permit empty groups to be handled gracefully? ...or is this a happy accident?

If this is a happy accident, I would be curious to know: are there are any current plans to change how things work in this regard?

✨ Thank you kindly!

--
Brie

---

A few examples to illustrate what I mean:

# cat spot.yml
---
user: cutecat
ssh_key: "~/.ssh/mykey"
ssh_shell: "/bin/bash"
local_shell: "/bin/bash"
inventory: inventory.yml

task:
  - name: 📅 Check the date
    script: date
  - name: ✨ check the uptime
    script: uptime
# cat inventory.yml
groups:
 web-servers: []  
 gpu-nodes: [] 
 db-servers:
 - host: 1.2.3.4
   name: db1
 queue-schedulers:
 - host: 1.2.3.4
   name: pbs0
 - host: 5.6.7.8
   name: pbs1           

Given spot.yml and inventory.yml like the ones above...

Target a group with no hosts

# spot -p spot.yml -i inventory.yml -t gpu-nodes --ssh-agent     --dbg
2025/06/25 09:14:39.251 [DEBUG] request to load playbook "spot.yml"
2025/06/25 09:14:39.254 [INFO]  playbook loaded with 1 tasks
2025/06/25 09:14:39.254 [DEBUG] load command "📅 Check the date" (task: default)
2025/06/25 09:14:39.254 [DEBUG] load command "✨ check the uptime" (task: default)
2025/06/25 09:14:39.254 [DEBUG] inventory location "inventory.yml"
2025/06/25 09:14:39.254 [INFO]  inventory loaded with 3 hosts
2025/06/25 09:14:39.261 [INFO]  ssh key: /Users/plop/.ssh/mykey
2025/06/25 09:14:39.262 [DEBUG] use private key "/Users/plop/.ssh/mykey"
2025/06/25 09:14:39.262 [DEBUG] use ssh agent
2025/06/25 09:14:39.262 [DEBUG] runner created: concurrency:1, connector: ssh connector with private key /Users/b.., timeout 30s, agent true, ssh_shell:"", verbose:false, dry:false, only:[], skip:[]
2025/06/25 09:14:39.262 [DEBUG] task "default" has 2 commands
2025/06/25 09:14:39.262 [DEBUG] target "gpu-nodes" found as group in inventory: []
2025/06/25 09:14:39.262 [DEBUG] target hosts (0) []
2025/06/25 09:14:39.262 [INFO]  completed: hosts:0, commands:0 in 0s
2025/06/25 09:14:39.262 [INFO]  completed all 1 targets in 0s
#                                                            

Target a group that is populated and a group with no hosts

spot -p spot.yml -i inventory.yml -t gpu-nodes -t queue-schedulers --ssh-agent     --dbg                                                     
spot master-70eea92-20250314T201823
2025/06/25 09:18:14.136 [DEBUG] request to load playbook "spot.yml"
2025/06/25 09:18:14.137 [INFO]  playbook loaded with 1 tasks
2025/06/25 09:18:14.137 [DEBUG] load command "📅 Check the date" (task: default)
2025/06/25 09:18:14.137 [DEBUG] load command "✨ check the uptime" (task: default)
2025/06/25 09:18:14.137 [DEBUG] inventory location "inventory.yml"
2025/06/25 09:18:14.138 [INFO]  inventory loaded with 3 hosts
2025/06/25 09:18:14.140 [INFO]  ssh key: /Users/plop/.ssh/mykey
2025/06/25 09:18:14.140 [DEBUG] use private key "/Users/plop/.ssh/mykey"
2025/06/25 09:18:14.140 [DEBUG] use ssh agent
2025/06/25 09:18:14.140 [DEBUG] runner created: concurrency:1, connector: ssh connector with private key /Users/b.., timeout 30s, agent true, ssh_shell:"", verbose:false, dry:false, only:[], skip:[]
2025/06/25 09:18:14.140 [DEBUG] task "default" has 2 commands
2025/06/25 09:18:14.140 [DEBUG] target "gpu-nodes" found as group in inventory: []
2025/06/25 09:18:14.140 [DEBUG] target hosts (0) []
2025/06/25 09:18:14.140 [INFO]  completed: hosts:0, commands:0 in 0s
2025/06/25 09:18:14.140 [DEBUG] task "default" has 2 commands
2025/06/25 09:18:14.140 [DEBUG] target "queue-schedulers" found as group in inventory: [{Name:pbs0 Host:1.2.3.4 Port:22 User:cutecat Tags:[]} {Name:pbs1 Host:1.2.3.4 Port:22 User:cutecat Tags:[]}]
2025/06/25 09:18:14.140 [DEBUG] target hosts (2) [{Name:pbs0 Host:1.2.3.4 Port:22 User:cutecat Tags:[]} {Name:pbs1 Host:1.2.3.4 Port:22 User:cutecat Tags:[]}]
2025/06/25 09:18:14.140 [DEBUG] connect to "1.2.3.4:22" (pbs0), user "cutecat"
2025/06/25 09:18:14.140 [DEBUG] create ssh session to 1.2.3.4:22, user cutecat
2025/06/25 09:18:14.176 [DEBUG] ssh agent found at /private/tmp/com.apple.launchd.r95y5ZJNvT/Listeners
2025/06/25 09:18:14.605 [DEBUG] ssh session created to 1.2.3.4:22
[pbs0 1.2.3.4:22] run task "default", commands: 2
2025/06/25 09:18:14.605 [INFO]  run command "📅 Check the date" on host "1.2.3.4:22" (pbs0)
2025/06/25 09:18:14.605 [DEBUG] execute script "📅 Check the date" on 1.2.3.4:22
2025/06/25 09:18:14.605 [DEBUG] command "📅 Check the date" is single line, using script string
2025/06/25 09:18:14.605 [DEBUG] run /bin/bash -c 'date'
2025/06/25 09:18:14.605 [DEBUG] run ssh command "/bin/bash -c 'date'" on 1.2.3.4:22
2025/06/25 09:18:15.205 [DEBUG] > /bin/bash -c 'date'
2025/06/25 09:18:15.248 [DEBUG] > Wed Jun 25 13:18:15 UTC 2025
[pbs0 1.2.3.4:22] completed command "📅 Check the date" {script: /bin/bash -c 'date'} (646ms)
2025/06/25 09:18:15.252 [INFO]  run command "✨ check the uptime" on host "1.2.3.4:22" (pbs0)
2025/06/25 09:18:15.252 [DEBUG] execute script "✨ check the uptime" on 1.2.3.4:22
2025/06/25 09:18:15.252 [DEBUG] command "✨ check the uptime" is single line, using script string
2025/06/25 09:18:15.252 [DEBUG] run /bin/bash -c 'uptime'
2025/06/25 09:18:15.252 [DEBUG] run ssh command "/bin/bash -c 'uptime'" on 1.2.3.4:22
2025/06/25 09:18:15.288 [DEBUG] > /bin/bash -c 'uptime'
2025/06/25 09:18:15.332 [DEBUG] >  13:18:15 up 1 day, 22:11,  0 users,  load average: 2.00, 1.56, 1.47
[pbs0 1.2.3.4:22] completed command "✨ check the uptime" {script: /bin/bash -c 'uptime'} (80ms)
[pbs0 1.2.3.4:22] completed task "default", commands: 2 (1.192s)
2025/06/25 09:18:15.332 [DEBUG] connect to "1.2.3.4:22" (pbs1), user "cutecat"
2025/06/25 09:18:15.332 [DEBUG] create ssh session to 1.2.3.4:22, user cutecat
2025/06/25 09:18:15.359 [DEBUG] ssh agent found at /private/tmp/com.apple.launchd.r95y5ZJNvT/Listeners
2025/06/25 09:18:16.211 [DEBUG] ssh session created to 1.2.3.4:22
[pbs1 1.2.3.4:22] run task "default", commands: 2
2025/06/25 09:18:16.212 [INFO]  run command "📅 Check the date" on host "1.2.3.4:22" (pbs1)
2025/06/25 09:18:16.212 [DEBUG] execute script "📅 Check the date" on 1.2.3.4:22
2025/06/25 09:18:16.212 [DEBUG] command "📅 Check the date" is single line, using script string
2025/06/25 09:18:16.212 [DEBUG] run /bin/bash -c 'date'
2025/06/25 09:18:16.212 [DEBUG] run ssh command "/bin/bash -c 'date'" on 1.2.3.4:22
2025/06/25 09:18:16.541 [DEBUG] > /bin/bash -c 'date'
2025/06/25 09:18:16.573 [DEBUG] > Wed Jun 25 13:18:16 UTC 2025
[pbs1 1.2.3.4:22] completed command "📅 Check the date" {script: /bin/bash -c 'date'} (361ms)
2025/06/25 09:18:16.573 [INFO]  run command "✨ check the uptime" on host "1.2.3.4:22" (pbs1)
2025/06/25 09:18:16.573 [DEBUG] execute script "✨ check the uptime" on 1.2.3.4:22
2025/06/25 09:18:16.573 [DEBUG] command "✨ check the uptime" is single line, using script string
2025/06/25 09:18:16.573 [DEBUG] run /bin/bash -c 'uptime'
2025/06/25 09:18:16.573 [DEBUG] run ssh command "/bin/bash -c 'uptime'" on 1.2.3.4:22
2025/06/25 09:18:16.598 [DEBUG] > /bin/bash -c 'uptime'
2025/06/25 09:18:16.631 [DEBUG] >  13:18:16 up 1 day, 22:11,  0 users,  load average: 0.18, 0.15, 0.10
[pbs1 1.2.3.4:22] completed command "✨ check the uptime" {script: /bin/bash -c 'uptime'} (57ms)
[pbs1 1.2.3.4:22] completed task "default", commands: 2 (1.298s)
2025/06/25 09:18:16.631 [INFO]  completed: hosts:2, commands:2 in 2.4s
2025/06/25 09:18:16.631 [INFO]  completed all 2 targets in 2.4s

Target all groups -- including groups with no hosts

# spot -p spot.yml -i inventory.yml -t all --ssh-agent
spot master-70eea92-20250314T201823
[db1 1.2.3.4:22] run task "default", commands: 2
[db1 1.2.3.4:22] completed command "📅 Check the date" {script: /bin/bash -c 'date'} (1.085s)
[db1 1.2.3.4:22] completed command "✨ check the uptime" {script: /bin/bash -c 'uptime'} (63ms)
[db1 1.2.3.4:22] completed task "default", commands: 2 (1.518s)
[pbs1 1.2.3.4:22] run task "default", commands: 2
[pbs1 1.2.3.4:22] completed command "📅 Check the date" {script: /bin/bash -c 'date'} (704ms)
[pbs1 1.2.3.4:22] completed command "✨ check the uptime" {script: /bin/bash -c 'uptime'} (61ms)
[pbs1 1.2.3.4:22] completed task "default", commands: 2 (1.458s)

# spot -p spot.yml -i inventory.yml -t all --ssh-agent     --dbg
2025/06/25 09:10:15.820 [DEBUG] request to load playbook "spot.yml"
2025/06/25 09:10:15.825 [INFO]  playbook loaded with 1 tasks
2025/06/25 09:10:15.825 [DEBUG] load command "📅 Check the date" (task: default)
2025/06/25 09:10:15.825 [DEBUG] load command "✨ check the uptime" (task: default)
2025/06/25 09:10:15.825 [DEBUG] inventory location "inventory.yml"
2025/06/25 09:10:15.825 [INFO]  inventory loaded with 3 hosts
2025/06/25 09:10:15.827 [INFO]  ssh key: /Users/plop/.ssh/mykey
2025/06/25 09:10:15.828 [DEBUG] use private key "/Users/plop/.ssh/mykey"
2025/06/25 09:10:15.828 [DEBUG] use ssh agent
2025/06/25 09:10:15.828 [DEBUG] runner created: concurrency:1, connector: ssh connector with private key /Users/b.., timeout 30s, agent true, ssh_shell:"", verbose:false, dry:false, only:[], skip:[]
2025/06/25 09:10:15.828 [DEBUG] task "default" has 2 commands
2025/06/25 09:10:15.828 [DEBUG] target "all" found as group in inventory: [{Name:db1 Host:1.2.3.4 Port:22 User:cutecat Tags:[]} {Name:pbs0 Host:1.2.3.4 Port:22 User:cutecat Tags:[]} {Name:pbs1 Host:1.2.3.4 Port:22 User:cutecat Tags:[]}]
2025/06/25 09:10:15.828 [DEBUG] target hosts (2) [{Name:db1 Host:1.2.3.4 Port:22 User:cutecat Tags:[]} {Name:pbs1 Host:1.2.3.4 Port:22 User:cutecat Tags:[]}]
2025/06/25 09:10:15.829 [DEBUG] connect to "1.2.3.4:22" (db1), user "cutecat"
2025/06/25 09:10:15.829 [DEBUG] create ssh session to 1.2.3.4:22, user cutecat
2025/06/25 09:10:15.863 [DEBUG] ssh agent found at /private/tmp/com.apple.launchd.r95y5ZJNvT/Listeners
2025/06/25 09:10:16.246 [DEBUG] ssh session created to 1.2.3.4:22
[db1 1.2.3.4:22] run task "default", commands: 2
2025/06/25 09:10:16.246 [INFO]  run command "📅 Check the date" on host "1.2.3.4:22" (db1)
2025/06/25 09:10:16.246 [DEBUG] execute script "📅 Check the date" on 1.2.3.4:22
2025/06/25 09:10:16.247 [DEBUG] command "📅 Check the date" is single line, using script string
2025/06/25 09:10:16.247 [DEBUG] run /bin/bash -c 'date'
2025/06/25 09:10:16.248 [DEBUG] run ssh command "/bin/bash -c 'date'" on 1.2.3.4:22
2025/06/25 09:10:16.765 [DEBUG] > /bin/bash -c 'date'
2025/06/25 09:10:16.806 [DEBUG] > Wed Jun 25 13:10:16 UTC 2025
[db1 1.2.3.4:22] completed command "📅 Check the date" {script: /bin/bash -c 'date'} (559ms)
2025/06/25 09:10:16.806 [INFO]  run command "✨ check the uptime" on host "1.2.3.4:22" (db1)
2025/06/25 09:10:16.806 [DEBUG] execute script "✨ check the uptime" on 1.2.3.4:22
2025/06/25 09:10:16.806 [DEBUG] command "✨ check the uptime" is single line, using script string
2025/06/25 09:10:16.806 [DEBUG] run /bin/bash -c 'uptime'
2025/06/25 09:10:16.806 [DEBUG] run ssh command "/bin/bash -c 'uptime'" on 1.2.3.4:22
2025/06/25 09:10:16.836 [DEBUG] > /bin/bash -c 'uptime'
2025/06/25 09:10:16.879 [DEBUG] >  13:10:16 up 1 day, 22:03,  0 users,  load average: 2.21, 1.54, 1.49
[db1 1.2.3.4:22] completed command "✨ check the uptime" {script: /bin/bash -c 'uptime'} (72ms)
[db1 1.2.3.4:22] completed task "default", commands: 2 (1.05s)
2025/06/25 09:10:16.880 [DEBUG] connect to "1.2.3.4:22" (pbs1), user "cutecat"
2025/06/25 09:10:16.880 [DEBUG] create ssh session to 1.2.3.4:22, user cutecat
2025/06/25 09:10:16.914 [DEBUG] ssh agent found at /private/tmp/com.apple.launchd.r95y5ZJNvT/Listeners
2025/06/25 09:10:17.754 [DEBUG] ssh session created to 1.2.3.4:22
[pbs1 1.2.3.4:22] run task "default", commands: 2
2025/06/25 09:10:17.754 [INFO]  run command "📅 Check the date" on host "1.2.3.4:22" (pbs1)
2025/06/25 09:10:17.754 [DEBUG] execute script "📅 Check the date" on 1.2.3.4:22
2025/06/25 09:10:17.754 [DEBUG] command "📅 Check the date" is single line, using script string
2025/06/25 09:10:17.754 [DEBUG] run /bin/bash -c 'date'
2025/06/25 09:10:17.754 [DEBUG] run ssh command "/bin/bash -c 'date'" on 1.2.3.4:22
2025/06/25 09:10:18.436 [DEBUG] > /bin/bash -c 'date'
2025/06/25 09:10:18.474 [DEBUG] > Wed Jun 25 13:10:18 UTC 2025
[pbs1 1.2.3.4:22] completed command "📅 Check the date" {script: /bin/bash -c 'date'} (720ms)
2025/06/25 09:10:18.474 [INFO]  run command "✨ check the uptime" on host "1.2.3.4:22" (pbs1)
2025/06/25 09:10:18.474 [DEBUG] execute script "✨ check the uptime" on 1.2.3.4:22
2025/06/25 09:10:18.474 [DEBUG] command "✨ check the uptime" is single line, using script string
2025/06/25 09:10:18.474 [DEBUG] run /bin/bash -c 'uptime'
2025/06/25 09:10:18.474 [DEBUG] run ssh command "/bin/bash -c 'uptime'" on 1.2.3.4:22
2025/06/25 09:10:18.507 [DEBUG] > /bin/bash -c 'uptime'
2025/06/25 09:10:18.547 [DEBUG] >  13:10:18 up 1 day, 22:03,  0 users,  load average: 0.18, 0.15, 0.10
[pbs1 1.2.3.4:22] completed command "✨ check the uptime" {script: /bin/bash -c 'uptime'} (73ms)
[pbs1 1.2.3.4:22] completed task "default", commands: 2 (1.667s)
2025/06/25 09:10:18.547 [INFO]  completed: hosts:2, commands:2 in 2.7s
2025/06/25 09:10:18.547 [INFO]  completed all 1 targets in 2.7s

[umputun]

I looked into this, and the graceful handling of empty groups is natural behavior that emerges from how the code works.

When spot encounters an empty group, it returns an empty list of hosts which gets merged with other results. No special handling, no errors - unless ALL groups are empty, in which case you'll get a "no hosts found" error (which makes sense).

Since this behavior is useful (as you've noticed), I added tests in PR #303 to make sure we don't accidentally break it in the future. The tests cover:

• Targeting only empty groups → error as expected
• Mix of empty and populated groups → works fine, only populated groups contribute hosts
• The "all" target with empty groups present → works normally

So yes, you can safely continue using empty groups in your inventory. It's now part of the tested behavior.

[bbbbbrie]

✨ Thank you very much!

So yes, you can safely continue using empty groups in your inventory. It's now part of the tested behavior.

🎊 That is fantastic news. Thank you very kindly for your quick response and action here!

✅ I'm marking this as the answer!