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Detect accessory image changes during boot #1808

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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 (#{running_image} → #{accessory.image}), run `kamal accessory reboot #{name}` to update"
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Copilot AI Mar 21, 2026

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The raised "image has changed" error doesn't include which host triggered the mismatch. Since accessories can run on multiple hosts, this can be hard to act on when only some hosts are stale. Consider including host in the message (or collecting all mismatching hosts/images and raising once after the on(hosts) block).

Suggested change
raise "Accessory `#{name}` image has changed (#{running_image} → #{accessory.image}), run `kamal accessory reboot #{name}` to update"
raise "Accessory `#{name}` image has changed on host #{host} (#{running_image} → #{accessory.image}), run `kamal accessory reboot #{name}` to update"

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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(", ")}, already running with the correct image", :yellow
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accessory.info(all: true, ...) uses docker ps -a, so it will match stopped containers as well as running ones. The skip message says "already running with the correct image", which can be inaccurate when a container exists but is not running; consider wording that reflects "container already exists" (or switch the existence check to running-only if that’s the intent).

Suggested change
say "Skipping booting `#{name}` on #{booted_hosts.sort.join(", ")}, already running with the correct image", :yellow
say "Skipping booting `#{name}` on #{booted_hosts.sort.join(", ")}, container already exists with the correct image", :yellow

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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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36 changes: 36 additions & 0 deletions test/cli/accessory_test.rb
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Expand Up @@ -19,6 +19,42 @@ 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 (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
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This test mutates the global Thread.report_on_exception and then forces it back to true in ensure. To avoid leaking global state across the suite (especially if another test sets it differently), save the original value and restore that value in the ensure block instead of always setting true.

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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 "already running 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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