From c138f58b21edb574b101588f6fc61dce8a98ed3e Mon Sep 17 00:00:00 2001
From: Tom Clegg <tom@curii.com>
Date: Mon, 23 Jan 2023 10:31:41 -0500
Subject: [PATCH] 19320: Log instance price changes in crunch-run.txt.

Arvados-DCO-1.1-Signed-off-by: Tom Clegg <tom@curii.com>
---
 lib/cloud/price.go              |  4 ++--
 lib/cloud/price_test.go         | 32 ++++++++++++++++++++++++++++++++
 lib/crunchrun/crunchrun.go      | 10 ++++++++++
 lib/crunchrun/crunchrun_test.go | 11 ++++++++++-
 4 files changed, 54 insertions(+), 3 deletions(-)
 create mode 100644 lib/cloud/price_test.go

diff --git a/lib/cloud/price.go b/lib/cloud/price.go
index 234564b684..59f5afc94b 100644
--- a/lib/cloud/price.go
+++ b/lib/cloud/price.go
@@ -10,9 +10,9 @@ import (
 
 // NormalizePriceHistory de-duplicates and sorts instance prices, most
 // recent first.
-//
-// The provided slice is modified in place.
 func NormalizePriceHistory(prices []InstancePrice) []InstancePrice {
+	// copy provided slice instead of modifying it in place
+	prices = append([]InstancePrice(nil), prices...)
 	// sort by timestamp, newest first
 	sort.Slice(prices, func(i, j int) bool {
 		return prices[i].StartTime.After(prices[j].StartTime)
diff --git a/lib/cloud/price_test.go b/lib/cloud/price_test.go
new file mode 100644
index 0000000000..e2a4a7e13c
--- /dev/null
+++ b/lib/cloud/price_test.go
@@ -0,0 +1,32 @@
+// Copyright (C) The Arvados Authors. All rights reserved.
+//
+// SPDX-License-Identifier: AGPL-3.0
+
+package cloud
+
+import (
+	"testing"
+	"time"
+
+	. "gopkg.in/check.v1"
+)
+
+func Test(t *testing.T) { TestingT(t) }
+
+type cloudSuite struct{}
+
+var _ = Suite(&cloudSuite{})
+
+func (s *cloudSuite) TestNormalizePriceHistory(c *C) {
+	t0, err := time.Parse(time.RFC3339, "2023-01-01T01:00:00Z")
+	c.Assert(err, IsNil)
+	h := []InstancePrice{
+		{t0.Add(1 * time.Minute), 1.0},
+		{t0.Add(4 * time.Minute), 1.2}, // drop: unchanged price
+		{t0.Add(5 * time.Minute), 1.1},
+		{t0.Add(3 * time.Minute), 1.2},
+		{t0.Add(5 * time.Minute), 1.1}, // drop: duplicate
+		{t0.Add(2 * time.Minute), 1.0}, // drop: out of order, unchanged price
+	}
+	c.Check(NormalizePriceHistory(h), DeepEquals, []InstancePrice{h[2], h[3], h[0]})
+}
diff --git a/lib/crunchrun/crunchrun.go b/lib/crunchrun/crunchrun.go
index 1dd232d3ed..1f130a5b10 100644
--- a/lib/crunchrun/crunchrun.go
+++ b/lib/crunchrun/crunchrun.go
@@ -2251,7 +2251,17 @@ func (cr *ContainerRunner) loadPrices() {
 	}
 	cr.pricesLock.Lock()
 	defer cr.pricesLock.Unlock()
+	var lastKnown time.Time
+	if len(cr.prices) > 0 {
+		lastKnown = cr.prices[0].StartTime
+	}
 	cr.prices = cloud.NormalizePriceHistory(append(prices, cr.prices...))
+	for i := len(cr.prices) - 1; i >= 0; i-- {
+		price := cr.prices[i]
+		if price.StartTime.After(lastKnown) {
+			cr.CrunchLog.Printf("Instance price changed to %#.3g at %s", price.Price, price.StartTime.UTC())
+		}
+	}
 }
 
 func (cr *ContainerRunner) calculateCost(now time.Time) float64 {
diff --git a/lib/crunchrun/crunchrun_test.go b/lib/crunchrun/crunchrun_test.go
index 1e3b2eb5c1..a5045863b0 100644
--- a/lib/crunchrun/crunchrun_test.go
+++ b/lib/crunchrun/crunchrun_test.go
@@ -12,6 +12,7 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
+	"log"
 	"os"
 	"os/exec"
 	"regexp"
@@ -2076,7 +2077,10 @@ func (s *TestSuite) TestCalculateCost(c *C) {
 	defer func(s string) { lockdir = s }(lockdir)
 	lockdir = c.MkDir()
 	now := time.Now()
-	cr := ContainerRunner{costStartTime: now.Add(-time.Hour)}
+	cr := s.runner
+	cr.costStartTime = now.Add(-time.Hour)
+	var logbuf bytes.Buffer
+	cr.CrunchLog.Immediate = log.New(&logbuf, "", 0)
 
 	// if there's no InstanceType env var, cost is calculated as 0
 	os.Unsetenv("InstanceType")
@@ -2106,6 +2110,7 @@ func (s *TestSuite) TestCalculateCost(c *C) {
 	// next update (via --list + SIGUSR2) tells us the spot price
 	// increased to $3/h 15 minutes ago
 	j, err = json.Marshal([]cloud.InstancePrice{
+		{StartTime: now.Add(-time.Hour / 3), Price: 2.0}, // dup of -time.Hour/2 price
 		{StartTime: now.Add(-time.Hour / 4), Price: 3.0},
 	})
 	c.Assert(err, IsNil)
@@ -2113,6 +2118,10 @@ func (s *TestSuite) TestCalculateCost(c *C) {
 	cr.loadPrices()
 	cost = cr.calculateCost(now)
 	c.Check(cost, Equals, 1.0/2+2.0/4+3.0/4)
+
+	c.Logf("%s", logbuf.String())
+	c.Check(logbuf.String(), Matches, `(?ms).*Instance price changed to 1\.00 at 20.* changed to 2\.00 .* changed to 3\.00 .*`)
+	c.Check(logbuf.String(), Not(Matches), `(?ms).*changed to 2\.00 .* changed to 2\.00 .*`)
 }
 
 type FakeProcess struct {
-- 
2.30.2