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Detect accessory image changes during boot #1808

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8a2e132
Detect accessory image changes during boot and raise actionable error
gmautner Mar 21, 2026
e7a084c
Address review feedback: include host in error, fix skip message
gmautner Mar 21, 2026
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10 changes: 8 additions & 2 deletions lib/kamal/cli/accessory.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -13,11 +13,17 @@ def boot(name, prepare: true)
with_accessory(name) do |accessory, hosts|
booted_hosts = Concurrent::Array.new
on(hosts) do |host|
booted_hosts << host.to_s if capture_with_info(*accessory.info(all: true, quiet: true)).strip.presence
if capture_with_info(*accessory.info(all: true, quiet: true)).strip.presence
running_image = capture_with_info(*accessory.running_image).strip.presence
Comment on lines +16 to +17
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Copilot AI Mar 21, 2026

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The container existence check uses docker ps -a -q --filter label=service=..., but the follow-up docker inspect targets service_name (container name). If a container matches the label but is not named exactly service_name (e.g., renamed/manual container), docker inspect will fail and abort boot. Consider capturing the container id(s) from accessory.info(...) and inspecting that id (or first id) instead, so the inspect target matches the existence filter.

Suggested change
if capture_with_info(*accessory.info(all: true, quiet: true)).strip.presence
running_image = capture_with_info(*accessory.running_image).strip.presence
container_ids = capture_with_info(*accessory.info(all: true, quiet: true)).strip
if container_ids.present?
container_id = container_ids.split(/\s+/).first
running_image = capture_with_info("docker", "inspect", "--format", "{{.Config.Image}}", container_id).strip.presence

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if running_image && running_image != accessory.image
raise "Accessory `#{name}` image has changed on host #{host} (#{running_image} → #{accessory.image}), run `kamal accessory reboot #{name}` to update"
end
booted_hosts << host.to_s
end
end

if booted_hosts.any?
say "Skipping booting `#{name}` on #{booted_hosts.sort.join(", ")}, a container already exists", :yellow
say "Skipping booting `#{name}` on #{booted_hosts.sort.join(", ")}, container already exists with the correct image", :yellow
hosts -= booted_hosts
end

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4 changes: 4 additions & 0 deletions lib/kamal/commands/accessory.rb
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Expand Up @@ -91,6 +91,10 @@ def ensure_local_file_present(local_file)
end
end

def running_image
docker :inspect, service_name, "--format '{{.Config.Image}}'"
end

def pull_image
docker :image, :pull, image
end
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37 changes: 37 additions & 0 deletions test/cli/accessory_test.rb
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Expand Up @@ -19,6 +19,43 @@ class CliAccessoryTest < CliTestCase
end
end

test "boot with image changed" do
Thread.report_on_exception = false

SSHKit::Backend::Abstract.any_instance.stubs(:capture_with_info)
.with(:docker, :ps, "-a", "-q", "--filter", "label=service=app-mysql")
.returns("abc123")

SSHKit::Backend::Abstract.any_instance.stubs(:capture_with_info)
.with(:docker, :inspect, "app-mysql", "--format '{{.Config.Image}}'")
.returns("private.registry/mysql:5.6")

exception = assert_raises do
run_command("boot", "mysql")
end

assert_includes exception.message, "Accessory `mysql` image has changed on host"
assert_includes exception.message, "(private.registry/mysql:5.6 → private.registry/mysql:5.7)"
assert_includes exception.message, "run `kamal accessory reboot mysql` to update"
ensure
Thread.report_on_exception = true
end

test "boot with same image" do
SSHKit::Backend::Abstract.any_instance.stubs(:capture_with_info)
.with(:docker, :ps, "-a", "-q", "--filter", "label=service=app-mysql")
.returns("abc123")

SSHKit::Backend::Abstract.any_instance.stubs(:capture_with_info)
.with(:docker, :inspect, "app-mysql", "--format '{{.Config.Image}}'")
.returns("private.registry/mysql:5.7")

run_command("boot", "mysql").tap do |output|
assert_match "container already exists with the correct image", output
assert_no_match(/docker run/, output)
end
end

test "boot all" do
Kamal::Cli::Accessory.any_instance.expects(:directories).with("mysql")
Kamal::Cli::Accessory.any_instance.expects(:upload).with("mysql")
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